SomeWhereOverTheRainBow
Part of the Furniture
I don't know how using AdGuardsHomes DHCP solved your router issues. you apparently are using a buggy option inside your dnsmasq.nevermind. i've found the bug. i have disabled the router's dhcp and enabled adguards. rebooted the router and now all clients are conected.
Code:
dhcp-option=lan,42,0.0.0.0
Nvm,
0.0.0.0 is a special case address used to represent the machine hosting dnsmasq. (kind of like :: for ipv6).