X mirror & Topology mirror don't work

I have a mesh with an armature modifier on it, but when I go into edit mode X mirror and Topology mirror don’t work.
Is it because my mesh has an armature modifier?
Thank in advance.

My experience with X-mirror has been than it tends to stop working and I cannot tell why. I just added an armature to the default cube and X-mirror kept working so I don’t think that your armature itself is the root cause.

In attachment I send a .blend file.
I made the following steps:

  1. in edit mode I moved the default cube.
  2. I created the armature
  3. I selected the cube then the armature and parented with automatic weights
  4. I added a mirror modifier to the cube and applied it


X-mirror.blend (474 KB)

If Topology mirror is not selected everything works well, what is the use of topology mirror?

If the shape of the mesh is asymmetrical, but the topology is still symmetrical, you can still mirror left & right.

example: add a monkey head. Select some vertices on ONLY 1 side and move them a bit. Enable X Mirror & Topology Mirror & move those vertices again. The vertices on the other side will snap to the same mirror location. X Mirror alone won’t do that

Is the topology of the cube object in the file X-mirror.blend not symmetrical?

I see what you mean. So the question is why does it work on Suzanne head and not a default cube. The tool description does mention “matching unique topology”, but I have no idea how ‘unique’ it should be.

Changing the cube a bit (creating differences in sides & front & side), copy these changes to the other side, and it actually starts working.