Hello there, thanks for the quick answer. Before atempting to create a post in here, I first searched for similar problems and already had done everything you said.
The problem still persists, even though I made sure every single keyframe is identical. You see, both the first and last keyframes are the same, but the character b_arm and b_hand still clips/moves on it's own during the transition (it moves/clips for a split second) and when I take a look at the first and last keyframe, I notice the last keyframes have both the b_arm and b_hand in a different position than what is shown on the first keyframe, even though I copy-pasted it!
So I'm still lost. Maybe I'm missing something. I'll try the CTRL+SHIFT+L thing and come here with a response. Thank you very much for your time.
Edit: It actually worked! Thank you very much! I really thought I had key everything at the beginning, it seems I had'nt, even though I checked it twice (?). Well, sorry for creating this post anyway and thanks for your help. I'm grateful.