Armature Exporting Issue

I am having trouble with a single bone not “functioning” as it seems to be rigid or misplaced. The blender file works fine but once I export to Unreal this single bone stops working.(Bicep.R)
Wondering if this is because of an export error. Some things that could help, I made the model and rig in Blender 2.8 . I had a mirror modifier for the mesh, and weight painting. I also duplicated the bones from the right side to the left and mirrored them.

Before I rotate the bicep.


After I rotate the bicep.

The left bicep works fine. Before rotation:

After Rotation:

I am new to the forums so if more info is needed please ask, this is my first project and anything helps.