Probably not your problem but if 8.8.8.8 has some wrong DNS record cached you can flush the cache for one name at dns.google/cache and for 1.1.1.1 at one.one.one.one/purge-cache/
There are also commands on each of the major operating systems to flush local caches.
It is also possible that DHCP or IPv6 router advertisements reset your manual DNS setting of 8.8.8.8 depending on how you set it.