I no longer have mobs spawning on my Realm, think it happened after last Aquatic update? I can walk safely at night anywhere without concern. Have hardly seen any fish so far overall, just a little at the initial release and dolphins seem to only shown one near my base and no where else. Mob spawners in caves work but thats it.
Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-21856.
Please add a vote and any new information to the main ticket, which will be updated accordingly.
As a temporary workaround, you might want to see if toggling the game difficulty to peaceful and back again helps with the mob spawning issue, as often there can be clusters of mobs hidden in caves.
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