This has happened a couple times already.
First off, chunks change back to a previous state
Example: Dungeon forgot it had been raided
Second: Chests decide to wait 5 seconds before opening
Third: Buttons decide you're not the boss anymore
Fourth: Downloading materials screen pops up for a while
(Don't respond)
Fifth: Chunk loading becomes horribly slow
Sixth: Massive frame problems
Seven: World-backup time

This is a horrible problem and is probably a duplicate post.