Video of the bug: https://files.catbox.moe/rtuju7.mp4 . I couldn’t upload directly to the forum.
I just had this happen to me (Rus). My opponent (English) runs their scout with a bunch of sheep into my TC. I kill the scout but I can’t take the sheep. From my perspective there is no indication why. The sheep just don’t change ownership.
In the replay I see that my opponent placed a mill blueprint next to the sheep and assigned the sheep to it. This stops me from taking them. In the game I did not see the mill.
The game on AOE4World: e00E's Game – AoE4 World