It could have happened, if Photos could not empty the recently Deleted album properly because of a damaged Photos Library. When Photos repaired or rebuild the library after a software update, the incorrectly deleted photos may have been recovered and the orphaned files restored to the Recently deleted album.
Another possibility is, tif you have enabled iCloud Photos recently on a differentdevice, where you still had these photos in the Recently deleted album. Then these photos will have been synced to all your devices.
Also, a few years before there has been a strange glitch. If the calendar has been set to a wrong date, when you trashed photos, they could remain invisible in recently Deleted after you corrected the date. and once the current date became the wrong date of the deletion the trashed photos would reappear. perhaps this has happened in your case as well.