While playing in the realm I purchased, a notification would pop up saying my "connection lost". Once reloading and rejoining, progress was lost. When manually disconecting and rejoining/reconnecting, a significant amount of progress was lost as well.
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Avoma
This appears to be a duplicate of REALMS-4224, which hasn't yet been resolved. If you have any additional information to provide regarding this issue, feel free to comment on the parent ticket. If you feel that this issue is affecting you, feel free to vote for the duplicated ticket, to give Mojang a basic idea of how many people are impacted by the problem. Just to further inform you, this will not determine how quickly the bug gets handled or fixed.
It happens to me as well