Mobs spawn but in such low numbers you have to hunt for 15+ mins in an unlit open field to find any hostile mobs. Fish and squids are also no longer spawning. In the picture attached the pond had 20+ squids spawning in it constantly, until server was updated to 1.13 pre3. I could walk away and come back and the squids would be repopulated. The server world was created in pre1 and mobs were spawning like normal until updated to pre3.
What version was this world created in? Also, what versions was this world upgraded to?