Crash if adding instrument to the middle of a score with many instruments

I can't reproduce. In order to investigate further, we'd need more specifics. Can you attach a particular score where this is a problem for you, and more precise steps (which instrument to add, where to move it to, etc)?

@Quaver Crafter: when doing this, are you in "Continuous View" or in "Page View"?
If you are in Continuous View, toggle in Page View, and let us know if you observe the same thing.

I suppose you have encounter this known issue (in Continuous View): #85046: Crash when adding/removing an instrument in Continuous view after autosave
You avoid it by adding/removing instruments in Page View.
If you find other thing, please reopen by providing, as requested previously, a specific score and detailed steps.
For now, marked as duplicate.

Chances are pretty good it was something about that specific score, or at least the sequence of events that got the score into the state it was in when you had 30+ instruments. Maybe you had previously added, removed, or rearranged staves in some particular order, maybe you had used "undo" as part of that process, maybe some of the staves were linked, maybe there were parts for some of the instruments, maybe the score had been saved & reloaded at some point in the process or maybe it hadn't, maybe you were in continuous versus page view, maybe you had "Hide empty staves" turned on, etc - all of these variables can affect the state the score is in. If you saw a crash, then certainly there is a bug in there (even low RAM shouldn't result in crashes, just poor performance). But the conditions that trigger it are rather more likely to be about the sorts of things I just mentioned than the actual number of instruments.

cadiz1 - our posts crossed, didn't mean to override the status. You may well be right about this being a duplicate. Still, probably just as well to leave this open as there have definitely been other bugs found and fixed with instrument adding/removal and it wouldn't surprise me too greatly to learn there are more.

It is also happening often here at least since MuseScore 2.1 (I didn't try older versions), but not always. Currently using MuseScore 2.3.1 Linux AppImage on Ubuntu 18.04. Always used the AppImage.

The question is: do you observe this in "Continuous View", or in "Page View"?
Please check this point first, and tell us.

Okay, the issue/crash in Continuous View, that you "use most often" is known since a while.

You wrote also. "In page view, the new stave and some neighboring staves would disappear, usually reappearing after I saved the file. Occasionally, the whole page would go blank."

This would be another issue. And so, it should deserve to be submitted in a new report (and when done, prouved, close this one)
But we need precise steps and a score to be able to reproduce (in particular, I don't recall right now of something about a blank page when adding/removing instruments in Page View, and that would return to the initial state after saving the score)

Closed due to lack of information. Please report, with precise steps to reproduce (and possibly a score), in a new thread, or reopen this thread, if the problem still troubles you in the latest version (3.4.2).