firewall and/or unbound dns trouble(?), slow, reloading websites

[caramba]

Finally got my OPNSense box and connected it. I ask you for help after hours of fruitless testing, internet access is not working correctly.

Google can be snappy, but clicking links result in loading for a long time, usually result in "we're having trouble getting this site". After ca 5 seconds it may reload and get the site, often without loading the whole page

This is via ethernet cable to LAN interface on this box(but same via wifi connected to same interface):
https://teklager.se/en/products/routers/apu2e4-open-source-router?

Variables tested:
Firefox, Chrome, Edge
Unbound enabled/not enabled, with/without forwarding(and Google DNS set), with/without blacklists

If I had to guess, firewall is somehow to blame. I tested traceroute from the menu and it worked sometimes, other times not.

I have two VLAN's on WAN as I need to split what comes from a fibre media converter(IPTV is VLAN 101, internet is 102). Any hints/tips on what/how to test further greatly appreciated.