It was just some particular preferences. Eventually so many added up that it had to go through before answering anything that it slowed things down considerably.
It was this feature. Perhaps it wasn’t stored locally, but it was almost getting unusable from lagging, with the computer fans or the HDD working hard, and turning it off improved things back to normal immediately. I don’t see why that would be if things were totally on their end, but I’m no information technician.