Basically the title, I have been experiencing this for the last two days. I was playing on iOS and I have ran into this issue in two different scenarios:

• Opponent casts Petty Theft on one of my permanents and the game crashes immediately. Relauching the game doesn’t help, the game inmediately crashes after reconnecting to the match while Petty Theft is on the stack. Once (I guess because of the priority timeout) Petty Theft leaves the stack, I was able to reconnect

• Opponent casts Brazen Borrower. Once the spell leaves the stack and BB ETB’s, the game crashes immediately. I was unable to rejoin the match, the game crashed multiple times when trying to rejoin. I was able to relaunch the client after a couple of minutes and it loaded the main screen (probably timed out of the match)