DNS leakage on multi-peer WireGuard VPN

My Spitz running firmware 3.215 reverts to using the the DNS servers assigned by DHCP, even though I’ve configured custom DNS servers in the GLiNet admin UI and selected “Override DNS Settings for All Clients”. If I toggle “Manual DNS Server Settings” off and back on, DNS queries will go to my custom servers until the WAN or LTE IP changes or renews, then it starts using the ISP’s DNS servers again.

My custom DNS servers are accessible over a WireGuard VPN that was set up through LuCI because the WireGuard client in the GLiNet UI can only support a single peer, but I need to route different subnets to different peers. The peer endpoints all have static IPs, so even if during startup DNS just wasn’t available for a few seconds until the peers were all connected, I still can’t see while it’s reverting to the WAN/LTE DNS servers.