[bbstar]

This is what happened.
1. I am South, the host, the dummy.
2. East loses connection and is replaced with a robot.
3. I "Remove and reserve" East player.
4. After some time East is back.
5. Meanwhile it is dummy's turn to play a forth card into a trick. (S, W, E agree).
6. North says he does not see East's card, and it is East turn to play.

Looks like some kind of a BBO Bug

I don't know exactly the time the last cards were played or if the East card was played by a robot or not.