I have had the same, happened once where I couldn't put anything in sideboarding game 2 and then could game 3. Then happened again a few days late where I couldn't sideboard both games 2 and 3. I was able to add or subtract cards on cards already in my deck, but nothing happened when I tapped the cards on my sideboard.
I have had the same, happened once where I couldn't put anything in sideboarding game 2 and then could game 3. Then happened again a few days late where I couldn't sideboard both games 2 and 3. I was able to add or subtract cards on cards already in my deck, but nothing happened when I tapped the cards on my sideboard.