I only have 1 mod that requires Blueprint on the server, The Outer End, and yet Blueprint keep spamming my log with

[co.te.bl.co.Blueprint/]: Received NBT for unknown Tracked Data: savage_and_ravage:invisible_due_to_mask

I know this is not a game breaking issue but it's still annoying to have my logs regularly taken up by this line, repeated many times
It seems to mostly happen during world generation

This is an issue caused by Savage and Ravage previously being in your world, so the game doesn't know how to read its saved data after it's removed.

The log spam should go away eventually after most of the entities that were around before you removed the mod are killed or reloaded.

Savage and Ravage has never been on the world. It's a brand new server