I get no internet warning to my 5GHz wifi router.
This is after clean install with format data and latest
modem firmware on my klte-phone
It was working fine on the los19 version.
I experienced this warning about no internet with previous versions of LOS before.
In all cases it was related either to the WAN connection, the router or the WiFi connection between the S5 and the AP/router and not related to LOS itself. Were able to solve, e.g. by forget and reconnect to the WiFi, restart router, etc.
No problems to connect my kltechn @LOS20 to a 5Ghz WiFi so far.
Good luck!