I'm quite certain that this is a fault from the computer or input device.
1. I'll go to a publish collection and while I'm looking at the published photos, they will suddenly appear as Modified Photos to Republish without any input from me. This can happen one at a time or all at once. I can mark them as Up to Date and clear them from republish status and then more will appear as Modified Photos to Republish!
There have been sporadic reports about this. Please add details of your issue and your vote to this bug report in the official Adobe feedback forum: Lightroom: Images unexpectedly appear under "Modified Photos to Re-Publish" | Photoshop Family Customer Community It's best to continue discussion of this problem in the bug-report topic, where others with the same problem and Adobe product developers will see it (product developers don't frequent this user-to-user forum).
You could try this workaround: Lightroom: Photos publish directly to "Modified Photos To Re-Publish" bug, with solution | Photoshop Family Customer Com… which has worked for at least two people. Add whether that works for you or not to the bug report.
I'm trying the fix but only my FB settings had Remove Person Info checked off. I've found other posts here that indicate this goes back to LRv5.1 - as I thought and it also means this happening on a different iMac since I was using my older computer back then.
I've found other posts here that indicate this goes back to LRv5.1
Reviewing the bug reports in the feedback forum, it appears there have been different bugs causing these symptoms over the years. Adobe fixed at least one of the LR 5 bugs in LR 6. So the posted workarounds don't work reliably.