This could be power saving
issue which is one of the usual causes (though rfkill
is not typical for that), try this (this worked for me in number of cases, or helped)…
To turn off powersave for network/wifi:
sudo vim /etc/NetworkManager/conf.d/default-wifi-powersave-on.conf
[connection]
wifi.powersave = 2
…‘2’ means ‘disable’ powersave
Also check here for an alternative Network is unavailable after sleep - #18 by brahma
But also very good catch by cscs, try that first.