During my last playthrough of murkwood arena, the game suddenly started treating one piece like a different one that I already had in my party. Originally I thought it was just a visual glitch but this piece behaved differently mechanically as well, including different moves and synergies, and switching it out of and back into my party did nothing. Later on it took on the appearance and behaviour of a different piece that I had just combined, so I thought it might be related to that and tried recording again, at which point my team was only 3 pieces instead of 5 for some reason. Eventually I removed all pieces from my team and put them back in, which fixed the issue. I do have video footage for this on google drive if that helps (link)