I found this when mirroring a simple box with a texture applied, see attached file.
The original object was mirrored with history on
Notice the copy has incorrect mapping
Also if you move the original object the mapping moves on the mirrored copy as it gets moved due to history.
I set mapping to box , turned on widget and scaled and moved the mapping widget to get the placement of the map on the object. Perhaps that will help.
MirrorTextureProb.3dm (205.0 KB)