I didn't see this discussed here yet but we ran into the desync issue over the weekend for the first time as we got to our first swamp biome, suddenly I couldn't chop logs or damage enemies so I Googled a bit and found the fix. It looks like the data rate limit of the game server is very low, I think by default it's 64KB/s, which with just discovering a new biome and now several new enemies, chopping trees and building we were hitting the limit and nothing new was coming or going through.
The fix is to edit a game dll and recompile it to raise the limit but I found a mod on NexusMods that does it without having to edit game code, what the mod does is raises the limit to 4x the original. We installed it today and went back to the same spot where the issue started and now I was receiving at 111KB/s and everything was working perfectly.
Fixing Valheim Dedicated Server Lag – Modify Send/Receive Limits
A Simple Fix To Valheim Multiplayer Desync