I don't wanna rule out anything that could work here! I wish I could provide better troubleshooting steps but since it's likely the World itself I don't know how to assist if it's corruption. ^TK
That's no good :/ Unfortunately, narrowing it down it sounds like it's likely the World and not the connection. I can't provide any troubleshooting steps to fix that :( ^TK
Then It may be something within the world causing issues even when you're offline. If its a Realm do you have a backup before a time you realized there was lag?^TK
If there was a lag before the big house it would point to interference between client and server. What troubleshooting steps have you tried and are you on Wifi or Hardwire? ^Tk
When an update that affects world generation is published, any chunks that have been previously explored will remain unchanged, and any unexplored chunks will be updated to generate the new features. ^TK