The problem below is reproducible in the attached save file (playing as me, Foddahedron, at [367,133,-75]).

Suddenly right-clicking on anything (crafting table, chests, etc.) stopped working correctly: now even after reloading there is a massive lag of 5 seconds or more on every right-click interaction. The game itself doesn't lag, just the response to the right-click (eg. the chest GUI comes up 5 seconds later, even after walking away). Loading a different save file all is fine, but reloading this one the lag is there just the same.

Prior to the problem, everything was working normally.

Originally some mods were installed, but I removed those (and all associated blocks/items). I have deleted all other region data to save space. None of this affected the reproducibility of the bug - load the attached save file and right click on a chest to see the problem.

The only unusual thing about this world that I can think of is that the rocks 100 or so below me are totally infested with silverfish (thanks to robotic mining), but it's been like that for ages with no ill effect).