A tip for anyone having such issues with wifi on linux: Is it a 2.4GHz network and is anyone using bluetooth (such as headphones)? They might be interfering with each other.
The iwlwifi kernel module has an option that tries to allow them to coexist, but it seems totally random whether or not you should have it on. Different bluetooth headphones also affect it in different ways (as I discovered a few weeks ago when I bought a different brand; with my usual the bluetooth would drop for about a minute then reconnect with no effect on the wifi, but with the new ones they would go crazy maintaining the connection, causing a lot of audio stuttering and extremely slow wifi).
The iwlwifi kernel module has an option that tries to allow them to coexist, but it seems totally random whether or not you should have it on. Different bluetooth headphones also affect it in different ways (as I discovered a few weeks ago when I bought a different brand; with my usual the bluetooth would drop for about a minute then reconnect with no effect on the wifi, but with the new ones they would go crazy maintaining the connection, causing a lot of audio stuttering and extremely slow wifi).
https://techvorm.com/fix-wifi-not-working-slows-ubuntu-bluet...
https://askubuntu.com/questions/1060094/bluetooth-audio-inte...