I have a notable update; I decided to try completely uninstalling roblox and this time wiping all of my local appdata (in %USERPROFILE%\AppData\Local\Roblox). This seems to have completely solved the issue. I understand that you guys are likely still wanting to diagnose whatever this is for a future update however, so I did back up the entire folder elsewhere first so it can either be restored or sent over for diagnosis.
Do you have anywhere secure I could send it to, or any other way that I could assist?
TL;DR for anyone else facing this exact issue and looking for a quick solution, delete your local roblox data after uninstalling (prior to reinstalling).
Apologies, I feel like I’m going back and forth so much with this issue. I’ve managed to repro the issue by changing my tab/section layout within roblox studio. The cause seems to be directly linked to me grouping the “toolbox” section with other sections and having the toolbox (now as a tab) hidden (the other tab in view). Closing the toolbox section entirely also fixes the issue.
Interestingly this doesn’t seem to have an impact in Roblox Player at all; so the issue I was having with that may yet have been caused by something else in my old/wiped roblox install (again, I do still have access to this if required)
TL;DR: The toolbox window has issues when it’s combined to make a tab (and not currently in view)
This is great information, thank you for posting not only the issue, but also the things that seem to work for you, so that other people can try. Really appreciated!
Unfortunately, I cannot run a microprofiler as the main issue is during the initial loading of a Studio instance.
What I can explain a bit though, is that Studio can sometimes take a long time, 20-45 minutes, to load a place. Usually these are larger places, and nothing else is happening on my PC at the time. I will say though, since making this comment, things have gotten a bit faster, so my initial concern there is lesser. However one major issue I still consistently have is the failure of Roblox (both studio and game client, but mostly studio) to load all of the unions in a place. Typically this happens on Studio; the place loads, taking some time, and for whatever reason some of the unions (or even most of them) will never load. You will get to the point where you can work in Studio as normal, however many of the unions are invisible. They are not corrupt, because the next time you open that same place in Studio or in a game client, they might load just fine. It’s sporadic.
I hope this helps to some degree, it’s a long standing issue and I’d love to see it fixed.