ok, after some time I realized the “trick”:
…to have IPv6 prefix delegation working with UPC/Vodafone and Compal router:
- factory reset the router (hint come from root.cz discussion)
- configure the stateful ipv6 configuration
- for WAN ensure that:
option reqprefix '64'is in config - for LAN include this:
option ip6assign '64'(or set it with GUI)
that’s it.