I just want to chime in and say I had the same issue with a world but I narrowed it down to a recently-placed large chest full of enchanted books. After I removed the chest and all the books, clearing my inventory, the game synced fine. Hard to tell exactly why this was the case, but it was consistently the problem with my world after many tests. Hope you solve it!
Extreme lag in the menus, feels like 5-10fps most of the time, sometimes slower. 3-4 seconds when clicking something. I have all render distance and effects turned down and makes no difference.
I just want to chime in and say I had the same issue with a world but I narrowed it down to a recently-placed large chest full of enchanted books. After I removed the chest and all the books, clearing my inventory, the game synced fine. Hard to tell exactly why this was the case, but it was consistently the problem with my world after many tests. Hope you solve it!