I’m having a problem where when I work with my model in Blender its pose is equal on both sides, but when I import to UE4 it gets this weird inconsistency in the left arm that lifts in in a weird way. Is this common? Is it something wrong I’m doing in blender, or UE4? Is there a quick fix for this in UE4? There is one simple idle animation attached to it, if that makes a difference.
I think it could bone axes not being the same in both arms, you can test that by ticking axes on the armature display options (just below bone layers) and if you notice you can recalculate roll by going into edit mode>armature options>bone roll>recalculate roll (or by pressing Ctrl + N in Blender 2.7 I don’t remember the shortcut in 2.8) and alining the most vertical bones with the +Y axis and the mostly horizontal ones with the +Z axis (those axes have given me the best results).
Another thing you may have going on is a weight affecting that part of the mesh on another bone, so check your weights and also your bone constraints if you used them, you may be telling that bone to copy the rotation of another.
Also if you are using IK, you may have to change the pole angle of your pole target, but I don’t think this is your case.
Anyway, if that doesn’t work, just let me know