Thommy, if you need another world to check, please let me know and I'll post mine as well.
Just switching the jar from 1.16.5 to 1.17 and starting the world will throw the errors every launch:
[media]
If it's of any help, here's some info on my server:
Linux mineos-tkldev 4.19.0-16-amd64 #1 SMP Debian 4.19.181-1 (2021-03-19) x86_64
Attempting to run vanilla 1.17.jar file after previously generating / running world on vanilla 1.16.5
Seed: [-7657594132119525537]
No data packs or modifications of any kind.
I'm experiencing the same errors as well. No data packs, vanilla server.
How does one optimize a world? Is this a possible fix?