Text shortcuts reset to older settings in System Preferences
Yes, they cross-pollinate from other devices. Mine come from my phone.

I'm really not certain why they don't correctly sync both ways. If I add one to the Mac it appears on the phone, but ones deleted from the Mac don't necessarily delete from the phone &amp; may later re-appear on the Mac.

I've found the best solution is to just make sure you've also deleted them from any other device.
Settings > General > Keyboards > Text Replacement