Gfw is mostly picky about anything udp or where both ports are unknown. Also if the known port (server) isn’t from a licensed block.

Basically there are heuristics that lead to either a reset, a temp block, or a perm block, but it seems to vary from time to time a lot.

Wireguard through gfw worked fine when I tried it. The other client did have a static IP and static Port tho, that probably helped