Hey. Thanks for the help.
I'm pretty sure I did that. But just to check, I booted up my original PS4, that I got my most recent UNO trophy on, and synched my trophies again. They didn't change and still show all but the Collector trophy as unlocked. I started up UNO again on my original PS4 to see if that prompted the trophy to pop. It didn't.
I then booted up my PS4 Pro and synched the trophies, but again it didn't change.
I'm not sure what triggers the Collector trophy to unlock, whether it is the game itself, or PSN when it detects all other trophies have been unlocked.
My thinking is that it is the game that triggers it, and because I got one trophy on my PS4 Pro (Nerves of Steel) and the game save and trophy list on my original PS4 didn't know at that time that I had unlocked that particular trophy, it didn't unlock the Collector trophy when I received the Flying Higher one.
If it is the game that triggers the Collector trophy, synching my trophies with PSN will make no difference, as the game hasn't unlocked it yet, so there is nothing to synchronise...if that makes sense?