Bugs happen. You are supposed to report them using the "Report Problem" tool in settings for the app.
I was able to get the same bug to occur on my phone after a couple of tries.
It is sort of an interesting question to wonder about how such a thing could occur.
Somebody else reported something similar:
https://www.chess.com/forum/view/help-support/illegal-computer-move
... and they said that computers would end creative play in chess. Seems like it's quite the opposite.
it's not en passant. there is no pawn there and it's not even on the 5th rank
it's not en passant. there is no pawn there and it's not even on the 5th rank
Did you save the game or get a screenshot?
There has been a bug on one of the apps, iOS I think, where the bots were making some illegal moves. Not sure if those have been fixed but app users should update, just in case.
I was playing as white against the computer on the Android app.
1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. d4 exd4 5. Nxd4 Bb4 6. Nxc6 Bxc3+ 7. bxc3 dxc6 8. Qxd8+ Kxd8 9. Bg5 Re8 10. Bd3 b5 11. O-O axb6????
The computer somehow captured an invisible piece on b6. Amazing! Does anyone else experience bugs with this software? How does this happen?