I just had the same experience as reported by others here.

Similar; couldn't do anything after and had to drop out of the game.

had the same problem

When I am playing a ranked best of 3 game, after the first one when I side cards into my deck, the game makes me confirm the changes and wait out the remaining time but when I'm actually playing the second game of 3 the changes I made are reverted. After the second game when I can side again the deck has the same cards it had in the first game and when I change cards the same thing happens: the game makes me save the changes to my deck, wait out the remaining time but in the actual match my deck has only the original cards and the side cards aren't present.
If a possible used italian language it would be better.
Thanks, Polo Stefano

For some reason, whenever I board in cards for game 2 and click the "done" button, the game isn't saving my new selections. While it does not happen every time, it does it around 80% of it. Log attached below. I really hope this gets resolved soon. Bo3 is where I and its costing us ranks. I don't want to be forced to only play Bo1 because of a bug. Appreciate all that you all do and best wishes. Stay safe, don't cough in peoples mouths. -Lantern16

Had the same thing happen wouldn't resume after restart.

I've been in the same situation. But my problem with Yorion and Standard Ranked game. After this one. I changed deck and experience same issue.

sideboard now shown on game 2 after I restart the client

After G2 i tried to sideboard but i could not because the sideboard screen froze and it was impossible to apply any changes to the deck.

Same issue but with Umori. It lets me sideboard but when I click Done is does some very fast flickering with the companion and I never draw my sideboarded cards. When I come back to sideboard for game 3 the sideboarded cards are _still_ in my sideboard as if I never put them in.

restarted game and sideboarding error prevented any changes. Sideboard clock didn't move I wasn't sure I could get back into the match.

after game one, I got this sideboard screen, was also unable to click on done, timer didn't move....

I experienced a bug several times after sideboarding with a Companion deck (Gyruda, Doom of Depths). The new state of the deck won't be saved, cards I sideboarded out are still in and new cards are missing.

Steps to reproduce:
Build a deck with Gyruda, Doom of Depths as a Companion and make a normal sideboard.
Play a game
Sideboard "odds" cards like Mystical Dispute
See the cards that should be missing
no sideboard cards in game 2 or 3

Expected Result:
good sideboard experience

Game froze against mechazilla, restarted game and sideboarding error prevented any changes. Sideboard clock didn't move I wasn't sure I could get back into the match.