This is not an isolated occurence
I'm using a well known provider in the UK (48 Mb s down & 8.9 Up) and the problem being described here has been evident for a few weeks - Download's speeds are behaving as expected but DNS look-up times are surprisingly slow - The general local WIFI congestion has not changed where I live. 32 bit or 64 bit PC's are behaving in the same way. I'm using DNS over https & 2.4 GHz networking The router has a separate broadcast SSID on 5 GHz. Up until now packet loss has not been a problem. I use both Windows & Linux at home. Surprisingly I recently performed a windows diagnostic check on the Win 7 Pro (an old standby ) and the Win 8.1 Dell Ethernet adaptors - Both tests revealed issues that I had not expected - (Windows auto fix resolved issues). I need to use the Dell for a prolonged period to verify that the problem described has been nailed.
The congestion does appear to be at DNS or protocol level. I'm not using especially new kit (positively ancient actually) I’m beginning to suspect that a) one more mesh networks have been set up in the neighbourhood, b) A firmware update has been applied to the router, c) Windows has subtly changed its stack handling functions. The last one being the most unlikely.
Finally the router is both IPV4 & IPV6 aware. I do not know how this impacts on the situation.
CAT III