This is happening since 3.2.6, when the dependencies were updated, including s9e's TextFormatter. With this update, emoji changed from EmojiOne to Twemoji.
Certain Emoji are no longer rendered probably.
Discussed with Joshy:
I've looked at Twemoji's code and the issue is that some of their emoji filenames keep the -fe0f at the end. Before that I assumed that it was systematically removed; In actuality, it's only removed if the sequence does not contain -200d.
I'll update the library soon but phpBB might be better off fixing it in userland. If you open an issue in the phpBB tracker I'll watch it and chime in as soon as I can.