Oh I think I figured out what the problem was, fingers xed!
Some time ago I had Rank Math plugin installed, and for some reason I added a featured SEO image on GD Detail page. I later removed Rank Math from the site completely.
However it looks like GD Detail page was somehow still pulling up ancient RM page Social featured image (all caches have been cleared many time since). This GD Detail featured image was interfering with GD post/listings featured image… and had facebook confused.
I have now, as an experiment:
— reinstalled RM
— added a new SEO featured image on GD Detail page
— checked Facebook and it was now scraping this NEWLY ADDED page featured image (instead of post/listing image)
— deactivated RM, purged all caches, several times
— checked Facebook — it STILL scraped this RM featured image, even though RM was no longer active
— reactivated RM, removed Social featured image on GD Detail page, purged caches
— Facebooking scraping OK now, post featured image showing fine
PS now that RM is deactivated once again, it is still showing bits of leftovers… I’ll attach screenshot