This could help me to find possible the issue, my suspicion is that there is an issue with how vlans or interfaces are created.
As advise I want to give to start simplier from br-lan first because besides the guest and br-guest are also associated with scripts and not just obey simple firewall zone forwards but traffic rules, you need to clone these rules to match with the new interfaces too, so best for me is to look this to.
please discard any mac addresses (also because for the safety on devices on ipv6 or for in the future on certain ipv6 setups as some devices derive their ip from their mac you don't want to give a attacker this information trust me)