I tried them first thanks and am yet to hear the sorry tale. I have little faith. I have a sore neck and use Dragon a lot. It was fine but on Scrivener 3 is a mess. The issue is between Scrivener and Dragon I suspect. They need to talk.
I am also having this issue. This is the real occurrence of a long-standing bug with Dragon but, for me, affects all applications on the Mac except Scrivener (prior to version 3) and TextEdit. Every other application has problems with insertion of unwanted characters or loss of cursor position, both of which are happening for me in Scrivener 3. I will have to continue using Scrivener 2. I sincerely hope this can be fixed. It is a major issue for people with disabilities.
I have contacted the support of Dragon and also the supportScrivener support. Scrivener support assured me that I should not be having a problem. I had a lot to do so I dumped scrivener for the time being, finished the books that I needed to write and I have now returned to Scrivener. Both DragonSupport and support assured me there is no problem. I am used to that with nuance who never seem to have a problem despite the fact that Dragon for Mac is ten years behind and remains a Beta product compared to the Windows product. Recently Nuance support was very helpful and they improved the results that I was getting using word enormously. I am writing this using DragonPad on the Mac and it’s not terrible. I managed to write three books between September last year and now using word. I have now spent two days using Dragon on Scrivener. It produces strange letters at the end of sentences and editing is worse than a nightmare. I regret to say support on scrivener which is usually excellent has missed the mark completely this time. Scrivener 3 does not work properly with Dragon. I repeat that Scrivener 3 does not work properly with Dragon dictate for Mac. Support will tell you it should work perfectly and they are using native Mac whatever it might be in it should work as well as scrivener two. I can assure you it does not and it will not. If you want to get a reasonable level of productivity you need to use word where it works perfectly well. I am happy to dictate and plan despite the rubbish that is produced in scrivener, but if I have to do serious writing I will definitely not waste my time in scrivener. It mangles editing and it simply wastes time. Please get your act together support and do something.
I’ve used Dragon for Mac in the past. I am sure that the OP has found the experiences recounted above very frustrating. But honestly, I wouldn’t look to Scrivener’s developers to improve the situation in the immediate future, especially with the other demands on their time at the moment with the launch of Scrivener 3, so I really wouldn’t blame them for the problems the OP has faced.
To tell the truth, I don’t know of any writing tool on the Mac, or on Windows for that matter, that has been modified simply to suit Dragon, although it may have happened. Personally I found using early versions of the most recent upgrade of Dragon for the Mac (6, I think) so frustrating for any purpose and at times, for me at least, just downright pointless, that currently I either use DragonPad and transfer, or use macOS’ own “free” dictation software (which though based, I understand, on Nuance’s technology, just seems more user-friendly), or I just type (though I recognise some can’t do this).
With earlier upgrades of Dragon, I gave up on Dragon for Mac (or whatever it was called at the time) and used Dragon Naturally Speaking on Parallels. But that also had problems for me. I do understand that the most recent versions of Dragon for Mac 6 are better. But it’s hard to be sure because the Dragon for Mac forum no longer seems to exist, and when it did exist it was largely filled with posters bitterly bemoaning the state of the application.
As some may be aware, the forums at http://www.knowbrainer.com also handle issues with Dragon for Mac software.
Nothing about the fundamental text entry mechanisms has changed between Scrivener 2 and Scrivener 3, except that Scrivener 3 uses the 64-bit Apple libraries. Our position on this problem is that it is coming from the Dragon side of things.
Katherine
Once again, I must agree with Katherine: Since Dragon exhibits these very same problems in a different editor (TextWrangler) it is unlikely in the extreme that Scrivener-specific code is causing them. It’s only showing up in Scrivener 3 (not Scrivener 2) and the only change is moving to the 64-bit text libraries? A Dragon problem. Dragon refuses to acknowledge it? Not a big surprise.
My only regret is that it’s too late to get my $280 back for Dragon.
This is a well-known glitch in Dragon Dictate and can appear in any program. The easiest way to correct this is to say Cache Document. The additional characters occur when Dragon loses its place in the application.
Additionally, I recommend upgrading to Scrivener 3. Dragon 6.0.8 is much more stable in the new version of Scrivener. It does not get lost as easily.
Yes, I agree. (This thread prompted me to try once again to use Dragon for Mac with Scrivener and other applications, and the results did indeed seem better. But I still don’t understand why users of Dragon, having, as Silverdragon indicates, paid large sums of money for the privilege, are forced to go through a beta-trial-that-isn’t on every occasion that Nuance tries to make a significant change to the software.)
To provide another potential clue, if you go back far enough in the forum archives you will find that there was a time when Scrivener 2 and Dragon did not play well together at all, and we frequently received requests to enable full text control—something that we cannot do, that phrase never meant something other developers could “enable” or somehow add to their software. At some point over the past few years, Nuance updated their website to include Scrivener in its full text control list, and things seemed to work well. I can only guess they tweaked their software to better work with Scrivener at some point, which is as far as I understand, what has always been necessary to get on that list.
We never did anything to get v2 working with it, to the best of my knowledge they never contacted us about it or worked with us in any way. There is likely then nothing that can be done from our end about v3 either—though I suppose the silver lining to all of this is that they are aware of us, and at some point the past put in the effort to make their software work with Scrivener. So the odds are it will happen again.
I can’t use Dragon in Composition Mode even though it works rest of the time. Why? What can I do to fix it?
Have you contacted Dragon support? As this thread notes, Scrivener doesn’t do anything special to “enable” Dragon, and Dragon doesn’t provide tools that would allow us to do so.
Katherine
There’s bad news on this front. Dragon for Mac was discontinued as of last month.
https://www.macrumors.com/2018/10/24/nuance-discontinues-dragon-mac/
If you bought in the 90/180 day window before the product was killed you can still get phone support, but I suspect that anyone else who wants support from Nuance can, well, go on wanting.
Yes, I’m bitter.
Wow, that surprises me. They’ve been around for years and many users love Dragon Dictate. Nuance’s reasons are apparently down to “constantly evaluating its product portfolio to see how we can best meet the needs of our customers and business”. Which I guess translates as Dragon Dictate for Mac is just not paying its way. A shame.
Yes, my thoughts were along those lines, particularly since Dragon didn’t work well with the 64 bit text engine. Evidently the maintenance stopped being worth the revenue. 
I’m sure their most profitable sectors are “enterprise” applications, like medical and legal dictation, and those are predominantly PC-based. “Consumer” dictation is being handled more and more competently by Apple’s own tools. Apple’s tools aren’t yet good enough for long form writing, but they’re fine for email and there just aren’t that many writers out there.
Katherine
Apparently not enough of them who can afford a $280 dictation program. 
That too.
Katherine
I used Dragon a lot on my last book. But found the random characters more than a little frustrating back then! I have, however, found Apple’s dictation works quite well if you use it in enhanced mode. It learns too, and becomes increasingly accurate over time. Perhaps worth giving it another try?
Apparently Dragon Dictate hasn’t updated to OS Mojave either which could be another issue.
Nuance discontinued Mac Dragon as of Oct. 22. Not wanting to update for Mojave (Sept. 24) was surely part of their reasoning.