If you are connected through WireGuard and ipleak.net shows DNS addresses that belong to your ISP (or that are you may have set up on your router or client device), then there is probably a DNS leak. If this did not happen previously when the router was on Firmware 3.215, then there could be a bug in Firmware 4.1.0 beta3.

What you mean by DNS being “not functional”. Do you mean that you cannot are not getting DNS resolution and, hence, cannot access websites … this could be a different issue?

If the DNS addresses belong to your VPN provider, then there is no DNS leak. Just to be sure, you can also test on dnsleak.com and dnsleaktest.com, which are what I use. They should all show the same DNS addresses.