Hey guys,
Sorry to update this threat few months later, but in case anyone else has this problem, we had a case with TAC escalations team and once they discussed the issue with R&D, this was their response (customer removed 8.8.8.8 dns server from the list (this is under gateway object in dashboard -> vpn clients -> office mode -> optional parameters). Customer had 3 servers there, 2 internal and then secondary backup as 8.8.8.8
R&D statement (which makes total sense). Also, just as a side note, you can leave google dns in web UI in dns list (hosts and dns)
**************************************
Here is RnD's statement:
You shouldn't mix internal and external DNS servers, it's not a backup\fallback server, the OS (any OS) treats them as equal and you can't rely on your internal domains resolved through the 'right' server.
You also don't have this server in the encryption domain so no reason for you to see these 8.8.8.8 DNS requests on your gateway. For another external fallback option the OS already has the DNS server configured on the physical interface so again, no point in having this one configured on the tunnel.
In iOS 16 Apple made some changes to prefer encrypted DNS when available and as 8.8.8.8 supports DoH/DoT it prefers to resolve addresses using this server.
In addition, in what clearly seems like an iOS bug, even if you have this server in the encryption domain they contact this DoH-supporting DNS server outside the VPN tunnel (it is encrypted DNS but still, it means internal resources will fail to resolve).
TL:DR
Adding 8.8.8.8 never actually did anything for you and in iOS 16 this just breaks things so it is simply recommended to remove it.
*******************************************************