Preface: I had launched and played on the server since the Nether Update on June 23rd with little to no issues.
From the update of 1.16 and to 1.16.1, Vanilla Tweaks updated many datapacks for the update and in order to bugfit and improve performance. On June 29th I launched the server to what seemed to be server lag as the time would lag back and any blocks I mined would reappear 10 seconds after I would break them. I then remembered that there was the 1.16.1 update and there were 2 datapacks from Vanilla Tweaks that had updates so I decided to update the game and datapack files, as well as installing papermc to the server to improve the performance. When I launched the server again about 2 hours later, I would join the game to limited chunks loaded, taking 5 minutes+ for my inventory and the spawn chunks to appear, and the same lag back and reappearing block lag. When I looked through the log to find what the issue was, I noticed in the error that the server believed that the datapacks I had deleted were not deleted and the cause of the server failing to load in the world. So I went back into the files and deleted the old datapacks multiple times, waiting 10+ minutes before restarting the server and each time the files would reappear. I downloaded the world, edited the files, loaded the world on single player which worked just fine, and re-uploaded the world to the site but even that would keep the files coming back.
Here is the most recent log from today:
Here is the specific error (1.0.0 is the old .zip file and 1.0.1 is the updated version)
[13:24:19] [Server-Worker-2/ERROR]: Couldn't load entity_type tag md:hostile_mobs as it is missing following references: minecraft:zombie_pigman (from count mob deaths v1.0.0.zip)
[This error is specifically referencing the change in the zombie_pigman to the new zombified_piglen with the 1.16 update]