Port sharing in router for IPv4 only

[alwi]

I installed Armbian_21.05.1_Odroidxu4_buster_legacy_4.14.222.img on HC2 and after this nextcloudpi with the actual curl script.

Portsharing Port 80 and 443 in Fritz!box 7460 worked only for IPv4.

An earlier installation of Armbian 14 months ago on the same machine worked under IPv4 and IPv6.

It is a mystery for me. Could anyone help?

http://ix.io/3nCZ

Thanks