Mirroring stopped working entirely after hours of using it without error. Blender 2.90 I have Googled the heck out of this and am still not finding my solution.
I'm several hours into modeling a character and suddenly mirroring doesn't work. For any vertex. For any axis. I have restarted Blender and reopened the project to no avail.
I am able to create new Mesh cubes in the same Collection and mirroring works on them.
I am new to Blender so I maybe I simply hit a hotkey by mistake? I have no idea what it could have been if that's the case.
I have found answers online saying to &quot;apply rotation,&quot; but this does nothing for my model. I have &quot;applied&quot; everything, all transforms. I haven't added a rig to it.
[Edit]: I have tried &quot;snap to symmetry&quot; on both the entire mesh and only half the mesh and neither works. Also, Sculpting in the sculpting tab works as expected. Still not working for modeling. It's like the functionality broke entirely or something.
[Edit 2]: When I &quot;Add&quot; a mesh to the scene in Edit mode, rather than object mode (so I technically add it to the character object), I am NOT able to mirror any axes on the newly added mesh. Only when I add a whole new object in Object mode.
[Edit 3]: Here's the .blend. The butt is lovingly modeled:

My project consists of 1 Collection containing 3 lights and my object. That is it.
Thank you!
Please let me know if there's any other information I can provide.
In edit mode (TAB), select all vertices (A). In mesh menu, click &quot;Symmetrize&quot; to fix the symmetry (use -X to +X or +X to -X). It should be fixed if you use X as mirroring axis.
While all vertices are selected, you should also fix your normals with Shift + N.
You should also try mirror modifier (but you have to delete 1 side).