So I've been creating a few characters for an animation and I've encountered an issue I've never had in blender before, when either copy pasting a mesh from separate files, using the mirror modifier, or applying automatic weights to armatures the results are always dodgy.
The results are similar to if I hadn't applied transform, but I've already tried that and it hasn't worked.
Before applying auto weights when connecting armature to mesh:
The mesh becomes displaced as if the global coordinates are off.
Same issue with mirroring and copy pasting objects across files