I found a similar issue MC-157265. Its status is closed. The overworld only has problems spawning when only 1 person is online in the overworld. As soon as another person enters the overworld, the issue is fixed and mobs spawn as normal.
I could not determine the solution since MC-157265 says closed to being a duplicate of other issues that are NOT the same as what we are experiencing. This world was created in 1.14.4 and never updated from a previous world. Mobs are not sticking around in unloaded chunks because it IMMEDIATELY fixes when 2 or more players are in the overworld.
For reference we are on Normal mode, mobSpawning game rule is true. Also, technically some mobs spawn on occasion. like maybe 5% of what it should be at best. The nether and the End dimension are unaffected.
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CubeTheThird
migrated
Happens to anyone.
https://www.dropbox.com/sh/8jqmpcfp0kqetmr/AADHGVFLQzdYrTvYDel6kiYba?dl=0 link to file
Vanilla server software.
Also, as an addendum, its quite possible that mobs aren't despawning in unloaded chunks when only one person is on. but like I said, the issue fixes itself as soon as a second person gets on.
Does this only occur for a specific player, or any?
Also, would it be possible to either attach the world file to this report, or upload it to an external service and link it here?
Lastly, is it the vanilla server software being used, or something else?