I have two templates. One uses normal multi-timbral instrument (similar as the ones from VSL but without the LogicPro bug ;-). The other one uses enivornment multi-instrument.
If you send me a project to take a look at, I will try to see if i can debug it. AU3 was supporting 127 tracks for me no problem, so I'm perplexed why its only working 84 for you. It might be something weird with the enviornment.
A little more background...
the original beta templates provided by VSL were most likely created with a version of LogicPro prior to 10.4.5. There are some known bugs when opening projects from before 10.4.5 in LogicPro 10.4.5+. It has to do with the way internal instruments are handled by LogicPro. 10.4.5 is when they bumped it up to 1000 instead of 255. But they changed some things while doing that and there are some odd bugs that can come up when you load an older project in LogicPro 10.4.5 and start adding/remove tracks, etc.. thigns can get out of wack, the metronome channel becomes hidden and other odd things. So..the beta templates from VSL may work, but then may run into that problem. I suggest VSL should rebuild them using a newer version of LogicPro or just use the ones I made, which are exactly the same, but I made mine with the new LogicPro. or follow the instructions to build up a template quickly from scratch yourself...but using the newer LogicPro...don't use the old templates that VSL originally provided for the reason I just said.
Now that being said, if you get more than 127 internal enviornment mixer strips all pointing to "Inst1", that is when LogicPro will vomit all over the place. So its possible just using the old templates might somehow accidentally get confused about that because of the LogicPro bugs I'm talking about. or its possible you ahve somehow accidentally created more enviornment mixer channels adn then when trying to create #85 you're really creating #128.
Lastly, I made a template using enviornment multi-instruments as the track interface, and this verison can handle 768 tracks per vePro instance...it doesn't come close to using up the 127 strip limit. So you might try that one too..but the downside is you have to have your tracks assigned to the enviornment objects rather then directly to the mixer strips.
Anyway, if you send me a project with the problem I am happy to take a look to see if I can figure out what is going on.
I doubt it has anything to do with too many synchron players..but VSL can say if there is a limit like that, but I would doubt it. But I am certain about the bugs in logicPro and I am certain that you can't have more than 128 internal enviornment mixer strips assigned to "Inst1".