Okay I think I can quantify what’s going on a little bit. This is a series of frankly serious issues that has persisted for at least the past several months of Unity updates. I think there’s some confusion in this thread because we’re all seeing slightly different artifacts, and I believe it’s coming from 3 separate bugs which may have to be dealt with individually.
1. Updating cloth to 2019
I haven’t tested this but from your first screenshot it looks like the weights got juggled around a bit upon update. You already pointed this out but I think it’s unrelated to the other issues.
2. Cloth stretches/distorts in the Editor
This is a weird one. I’ve tried tons of different combinations of modifiers/UV unwrapping in Blender to reproduce, and I have narrowed down the cause a little. It seems to be related to either mesh density or total vertex count. Take a look at this cube which is rigged to a single bone:
I had trouble reproducing it on a non-rigged object so I just weighted this cube to one bone. This allowed it to automatically enter as a Skinned mesh, as opposed to the Cloth generating one from a mesh filter/renderer. I’m using the solidify modifier to reproduce the cases that broke in my game. Now look what happens if I use a subdivision surface (a modifier that subdivides all polygons):
No cloth settings have changed, yet the stretching is now happening. So is something wrong with the subdivide modifier in Blender? I think so. This is the result I get when doing a “manual” subdivide smooth under the special menu:
It should be no surprise now that this is the result when I remove the Solidify modifier and manually extrude the rest, while leaving the subdivide modifier enabled:
This proves that it’s clearly not some combination of solidify/subdivision, but rather just an artifact of the subdivision. Now the most interesting part is when I apply the subdivision modifier:
The issue persists.
So what have we learned? The subdivision modifier does… something weird to the mesh. I was able to get distortion without the subdivision modifier by performing arbitrary steps of duplication and rotation, but sometimes it just won’t reproduce.
3. Cloth disappears during Play Mode
My best guess is that this happens when a “bugged” Cloth from Bug #2 is run with constraints active. This is what happens when Playmode is activated without constraints:
This is a capture from the first frame of playmode. After playing it falls down as you’d expect, no distortion. However, this is what happens when I add constraints to the top of the mesh vertices.
We get this buggy mess. Those black shapes are part of the cube. All I did differently is add a constraint of distance 0 to the top of the mesh, and you’d expect it to just stay in place. In fact, when tested on a non-bugged cube, that’s exactly what happens. So practically it makes sense to avoid the stretched/distortion bugged state that these objects get into.
Final Thoughts
It’s a bit complicated to explain all this over a Unity bug report, and I’m not sure if the cloth disappearing bug could be fixed thus fixing the rest of these… I’ll have to do more testing and see if I can get my mesh working by playing around with the subdivision and UVs. I’m not sure if other parameters such as skinned mesh vs. static will affect it, I really can’t afford to waste more time on this. I don’t know what else to do except bring it to Unity’s attention. I’ve voted on the issue tracker you listed so here’s hoping they investigate further and nail down the cause. I might report back if I can come up with a workaround for my cloth meshes.
If I get some time maybe I’ll write this script as it would be useful until the bug gets fixed.
