My Java edition Realms server (on name of MuMe) was temporary unavailable with this error message one of my players recorded. 
World is in operation FIXING since 2018-08-19T10:52:48.815Z (PT2H48M30.7155) - 500
There were no problems the last time he got online and as far as I know he should have been the last online (cant check as player activity hasn't been available for some time now...).
The next time he got online there was about +/- 3 hours of progress lost.

I also found 2 others on the Minecraft Reddit that has had this problem 2 days ago. But they said nothing about lost progress (or might not realized any). This error has not been mentioned anywhere else as far as I know.
https://www.reddit.com/r/Minecraft/comments/97yhzy/realms_world_is_in_operation_fixing/

I would like to know what happened, I am worried about my world and the stability of the Realms servers.
Could it have something to do with crashes we have been having since 1.13 came? Since 1.13 all the players on my server have seen full server crashed with "Connection lost. Timed out." error. Was still trying to figure out what triggered those crashes to give detailed reports on them. Is it possible you guys already fixed that with this?