I've been hit by this as a commercial balloon pilot. We were all pushed into getting the shiny new UK EASA BPL(Balloon Pilots Licence) at the back end of 2019 as we were informed we could no longer fly commercially after April 2020. This we were told would future proof us and allow us to play in Europe too. For another 35 quid we could keep our old UK CPLs for use in countries that accept them(Such as Myanmar where I spend my winters).
Anyway, now my lovely piece of A4 is now just expensive bog roll as I live in Germany and fly the summers in France.
Luckily I still have a French national licence which I'm currently transferring. It expired in June last year as I'd let it lapse due to the new UK licence. I was told by our man on the inside not to even mention the fact that I have a UK EASA licence and just to provide proof that I'd completed the requirements for the revalidation of my French licence and they'd then issue me an EASA equivalent on the back of it...However I suspect even the very friendly and easy going staff in the DSAC office in Marignane will find something that doesn't line up...