Also having this issue in Realm server with 1.2.3 (Bedrock) clients.
Blaze spawner was converted into a grinder and while initially working, now the moment a player enters the chunk in the Nether, the Realm crashes.
Currently one player is stuck in the chunk and crashes the Realm every time he attempts to join and any player attempting to enter the chunk crashes the Realm which restores itself to the last autosave before the crash.
Nickolas Laffen
Also having this issue in Realm server with 1.2.3 (Bedrock) clients.
Blaze spawner was converted into a grinder and while initially working, now the moment a player enters the chunk in the Nether, the Realm crashes.
Currently one player is stuck in the chunk and crashes the Realm every time he attempts to join and any player attempting to enter the chunk crashes the Realm which restores itself to the last autosave before the crash.
Clients include: XB1, Win10, IOS and Android.