I created animation with 2 armatures. In the screenshot below it is visible that animations (and armatures) are: pistol, hands. Pistol root is parent of wrist bones (so pistol root can control hands for easier animation).
To export my animation to game engine I need to combine both armatures. After doing Object -> Join I'm having this problem (first I selected Pistol armature, then Hands armature, then Object -> Join):
All animations after joining are off in some peculiar way. Basically offset for them is broken for some reason. If I try to manually move hands down (with Pistol root bone) - all hands animation is just turned off.
This video shows the process of joining: