Throughout the day, I have experienced lost progress in realms. Sometimes minutes' worth, but most recently it was an hour or more of work lost after I disconnected and re-connected.

Not sure how relevant this is, but my boyfriend loaded the nether for the first time on our server world earlier today since he was waiting for the update, and he has also been experiencing crashes with loss of data. We have a solid internet connection, and have been testing it all day. I figure our problems are either just traffic due to the update, or something wrong in the update itself, but either way hopefully this is a good enough description.