Attempting to sleep in a bed results in the message "You may not sleep now, there are monsters nearby" despite there being no monsters nearby (We are playing in Normal mode.)
We searched the surrounding caves for monsters using spectator mode, but found no monsters. We neutralised any mob spawners we were using, and it still did not allow us to sleep. In the end, we had to use commands to pass the night.
Trying to sleep in a different bed did not solve the issue.
Breaking the bed and replacing it did not solve the issue.
Disconnecting from the Realm, closing it and reopening it did solve the issue.
We did not have this issue for a time, but trying to sleep suddenly started giving us this message after a few minecraft weeks.