here is a test file just add multires modifier
do 2 subdiv in the multires (notice mesh not changing)
go to sculpt mode
crash

crashes after you go to sculpt mode.
works with no crash on 2.80 but crashes on 2.81

For the records, I think you may not even need the other modifiers, the multires alone seems to still break things. That said I need to rebuild blender with more libs to fully debug this, so considering the report triaged as it is.

Multires has a lot of issues and bugs when used combined with other modifiers. Maybe we can make it not crash by disabling some sculpting features in Multires (bad idea, as this is a unusual use case) or avoiding entering sculpt mode in some situations (like Multires + more modifiers or sculpting in a level other than the highest one).
I don't think we should spend time trying to debug and make proper fixes to bugs like this one (or doing any other Multires related development) before fixing T58473. Even if we fix all these crashes, Multires is going to keep breaking the models, making it unusable for its intended purpose. The end user is not going to get any real benefits from this development work.

Even if we fix all these crashes, Multires is going to keep breaking the models, making it unusable for its intended purpose. The end user is not going to get any real benefits from this development work.

I see your point, but I disagree here. Make it not crash is a real benefit, regardless of what made the users mix the modifiers. Broken files are ok-ish, lost work due to a crash is very costy in the end.

T58473 is worse than any crash we currently have in terms of losing work. Saving wrong information and corrupting a file without knowing it is always much worse than a crash (you can always recover the last saved version). Current Blender users know that Multires is not suitable for sculpting, but new users may lose days of work without noticing it with that bug.

This is probably not really related to this task, but in my opinion, a fix or workaround for T58473 should block the release. I'm not aware of any other bug in Blender that is damaging an area of the software as badly as this one. We need to acknowledge that we have the most basic and fundamental feature of any sculpting software broken, so anything built on top of that is not going to benefit anyone. During the 2.81 development, multiple developers spend time on Multires related projects (optimizing it, porting the tools, Quadriflow..) that no one is going to be able to use in a real use case just because of that bug. In my opinion, we should have a way to detect and make a plan for this kind of issue earlier to prevent this from happening again.

just a quick Note: the bug will not happen if you toggle all or one of the before modifiers. (show wrap, hide displace OR hide wrap, show displace )
also never noticed this warning before:

In T71503#809435, @Pablo Dobarro (pablodp606) wrote:

Multires has a lot of issues and bugs when used combined with other modifiers. Maybe we can make it not crash by disabling some sculpting features in Multires (bad idea, as this is a unusual use case) or avoiding entering sculpt mode in some situations (like Multires + more modifiers or sculpting in a level other than the highest one).
I don't think we should spend time trying to debug and make proper fixes to bugs like this one (or doing any other Multires related development) before fixing T58473. Even if we fix all these crashes, Multires is going to keep breaking the models, making it unusable for its intended purpose. The end user is not going to get any real benefits from this development work.

I m wondering why we are not doing full multires. overhaul? Note that Multires. is the only tool in Blender that can help us to get more than 20 Millions polygons with responsive 3d viewport. In stand of turn off some features in multires. or adding more features in sculpt mode it will be good to rework multires.
For you to know there is old users using Multires. even in this " broken" state.