HELP, can't rig mesh?

Hi, I tried everything to rig this mesh. I don’t know what happend.
I’ve been rigging for a long time but this never happend to me.
I used the mesh and rigged it like I always do with automatic weights, the mesh is symmetric, clean and I also merged by distance and deleted loose vertices. I also applied everything. I added bones and everything was fine with rigging. Then I wanted to correct one bone with the weights, and then suddently every bone didn’t worked and it always said “couldn’t find a solution for one or more bones”. I found out I can’t add any bones to the mesh, but 1 hour ago everything was fine. So, everything worked with the mesh before. Suddently I wanted to correct one bone and now everything is messed up. Why I can’t rig this mesh so suddently? Is it bc I enabled something? I don’t know. The mesh has no modifiers, nothing.

Please help, I need the mesh for a buyer who wants it quickly.

blenderhelp.blend (2.7 MB)

Edit: I scaled the mesh bigger and now it works again. I can’t believe this was the reason.

it looks like there’s no armature in your file, so hard to test. I’ve create an armature, deleted all previous vertex groups, then parented, and it seems to work fine… maybe share a file with an armature and describe precisely how to make it bug

When I scale the mesh bigger or smaller it works again (I don’t mean to apply the scale, I already applied the scale several times and it didn’t worked). But without scalling the mesh it didn’t worked with any armature. I wonder why. I guess it’s bc of my computer, I don’t know?? I also deleted all previous vertex groups. Weird!

oh ok, yes it’s always better to apply the scale