Seems like your router would have changed networks upon setting a DNS server, so probably similar to Can't setup network-wide DNS because of router - #8 by Bucking_Horn (not uncommon for TP-Link models).
Seems like your router would have changed networks upon setting a DNS server, so probably similar to Can't setup network-wide DNS because of router - #8 by Bucking_Horn (not uncommon for TP-Link models).