After the A20.4 update I experienced this error while playing in my friend's world. When this happened I couldn't move a few blocks from my spot as I would just rubber band back.
Our solution then was for her to reload her world so I can rejoin because I couldn't find her in the Friends Tab in the server list.
After joining, my character has reverted back to a certain state. Not back to level 1 but like back a few days of playtime. Before the error I was lvl132 and completed several quests but after I rejoined, it's as though I never completed any quests. It's back to when we last logged out a few days ago but I couldn't remember exactly when. I'm lvl131 again BUT my inventory was saved for some reason.
Days later we played again and even without encountering the error, my character's progress doesn't seem to be getting saved aside from inventory related stuff like selling or harvesting items. We thought nothing of it and decided to do some quests, one of them being a Fetch & Clear, which means me getting a White River Supplies Box. Hours into the game and voila! I get the error again and now I have a permanent White River Supplies in my inventory.
Here's my log: https://pastebin.com/q9uLFmad
Here's my friend's log: https://justpaste.it/3hjel
I asked around in discord and so far their solution for me was to start fresh OR as one told me "try to eliminate duplicate hidden blocks" on certain places as told by the log with errors on them. Though he's not sure if that will solve it.
So far I haven't tried the blocks thing yet.
I'm asking around here too and in the Steam Forum if anyone encountered anything similar or something exactly like this.
Thanks.

Our solution then was for her to reload her world so I can rejoin because I couldn't find her in the Friends Tab in the server list.
After joining, my character has reverted back to a certain state. Not back to level 1 but like back a few days of playtime. Before the error I was lvl132 and completed several quests but after I rejoined, it's as though I never completed any quests. It's back to when we last logged out a few days ago but I couldn't remember exactly when. I'm lvl131 again BUT my inventory was saved for some reason.
Days later we played again and even without encountering the error, my character's progress doesn't seem to be getting saved aside from inventory related stuff like selling or harvesting items. We thought nothing of it and decided to do some quests, one of them being a Fetch & Clear, which means me getting a White River Supplies Box. Hours into the game and voila! I get the error again and now I have a permanent White River Supplies in my inventory.
Here's my log: https://pastebin.com/q9uLFmad
Here's my friend's log: https://justpaste.it/3hjel
I asked around in discord and so far their solution for me was to start fresh OR as one told me "try to eliminate duplicate hidden blocks" on certain places as told by the log with errors on them. Though he's not sure if that will solve it.
So far I haven't tried the blocks thing yet.
I'm asking around here too and in the Steam Forum if anyone encountered anything similar or something exactly like this.
Thanks.