MAP-T IPv4 Ping Issues

Hi,
I'm successfully running MAP-T, everything looks to be working for v6 and v4 so far (www/ftp/ssh..) apart from ICMP for v4, for some reason I'm not able to ping IPv4 addresses.

I see the following error when I try.

Wed Apr 16 08:15:41 2025 kern.warn kernel: [64385.396685] [nat46] Could not translate v4->v6

Raspberry Pi 5 Model B Rev 1.0 (also tried on a Pi 4)
OpenWrt 24.10.0

I've also tried MAP-T with a Fritz5690 PRO and ping v4 works okay with that.

Any advise welcome.