A friend and I noticed yesterday that apparently the game won't load if you're accepting the ready check while you're inbox is open. Could that have been the case for you too?

We had this problem several times and only with an open inbox while we haven't yet encountered the same problem while the inbox was closed. So we think this might be linked?
Not sure if it's only a problem for ranked matches or if it'll happen for unranked matches too, since we didn't really test it. It was more like forgetting about it again and being reminded, by being stuck again.

Only solution was to either relogg and take the penalty as stated or to wait a few minutes until the match, that one couldn't see or play ended (explanation why we assume this in the spoiler+we got coffers in the mail). In this time it wasn't even possible for us to go through doors or do anything useful, because the prompt to interact just wouldn't show up or work.