Recently a new update has been released for the Minecraft Bedrock Edition. The only problem that the version number has decreased from 1.17.2 to 1.17.1, causing realms to be inaccessible as they are still on 1.17.2, while everyone else is still on 1.17.1.
REALMS-8576
Realms inaccessible due to update number reversing
Resolved
Invalid
0
1.17.10 is after 1.17.2. (10 > 2)
You need to have the realm owner log on with the updated version, or wait for the 48 hour automatic update.