I wouldn't count mouseslips as legitimately illegal moves either, they are also incredibly rare because most online players play with auto confinement to legal moves.

Moving through check definitely counts as as an example of a human knowing the rule and yet playing the move anyway. Which was the position you took when claiming humans would not do moves against rules they have learned.

In my experience sub 2000 players playing OTB informal chess do illegal moves fairly regularly, perhaps 1 in 50 games. Moving knights one square too far, slipping a bishop from one line to the next on a long diagonal. Castling after moving the king, not moving out of check, moving into check (especially by moving a pinned piece)

They all meet the criteria of knowing the rules and playing something else. Oftentimes people do this because they have a mistaken assumption about board state. I suspect the same is true for LLMs, they are making valid moves for what they mistakenly think the board is. That would be difficult to test, but I think possible with the right introspection tools.