One group with a paid, group subscription asked support about the instability, and was simply told their use case was unusual (writing conference papers with some git and some web editors?). They are now planning on moving away from using it.
That said, I actually don't think the integrated Overleaf editor is bad. They have Vim keystroke support, so I can fairly easily use it without much trouble on my end.
I’m not comfortable using it for extended work though. I miss things like surround text objects for TeX environments and macros (provided by evil-tex or vimtex), ergonomic entry of equations (provided by CDLaTeX or by the vimtex insert-mode bindings), autoformatting (provided by latexindent), and some navigational abilities (e.g. being able to jump to the documentation of TeX packages with a single keybinding). On top of that, there’s the missing general editor plugins… And at least on MacOS, their PDF viewer is quite blurry compared to the native viewers :)
With that said, I think Overleaf is great, and it’s made LaTeX itself much more accessible for a wider audience. But for me, it pales in comparison to a local Emacs or Vim configuration…