sideboard
I see similar issues posted, on android app can sideboard fine between game 1 and 2. Sideboarding between game 2 and 3 I removed a card from my deck and was unable.to put any from my sideboard back in. Could not submit a deck and was stuck on sideboarding screen. Restarted and was stuck on waiting screen for 15+ minutes. Restarted again and was finally back to home screen.

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Venski#90863 commented
After restarting the game on iOS I can't sideboard neither after game 1 nor after game 2.
If for any reason I lose connection to the Internet it's faster for me to switch off the phone wifi and restart the game. After restarting cards can no longer leave the side board. I can move cards away from the main deck, but after that I can't move cards to the deck and I can't submit the deck because it is no longer valid