4nes4snes - player 4 not read

[Roet-Ivar]

When flashing the 4nes4snes.bin onto this ch552 port 1 - 3 works perfectly but port 4 is not read at all on p1.7.
Swapping port 3 and 4 gives the same result, port 3 (which confirmed working) is not read on p1.7.

I've also replicated this beviour in a second ch552, nothing on p1.7.

Any ideas what's up?
Thanks!