Me and my friends have been playing on a realm since the day the 1.17 update came out and three times we have lost progress due to the realm crashing and disconnecting all of us for 15~ minutes. There's nothing specific that we do nor does it correspond to having multiple players online. The only thing that I can say has happened two of the times is I loaded a lot of new chunks while exploring and then sometime while I am returning or after I have returned the realm crashed. I have seen that this issue is marked as resolved in other bug reports but, that is not true. I haven't lost anything major but, I know if this bug isn't fixed that it could cause major progress loss to other people.