I notice that Stellarmate has been updated to Mate 18.04 and I am told 5ghz Wifi works.
I have tried this on a std Indi installation (Not Stellarmate) on Mate 18.04 and it doesn't (or didn't) what was changed on the Stellarmate version to make 5ghz work - if thats not giving away trade secrets - LOL
lol no "trade secrets", it's just plain 18.04. I suspect it might be some firmware issue? make sure to dist-upgrade after the initial installation so that the most recent kernel is installed.
Went back to basics down loaded latest Ubuntu Mate 18.04 (again) and ran through the APT Update etc etc (again) - wired works first time again.
Then tried 5ghz wireless it asked me 5 times for the password (each time was correct - even got the Wife to check) . Still US !
I have used 5ghz with all my computer kit - it all works but I cant get Ubuntu Mate 18.04 to work with 5GHZ using my standard TPLink kit
It even works with 2.4ghz on the same router (TPLINK dual band 5 and 2.4) - tried a different router(not TPLINK but dual band) - same. Even tried switching off security still asks again and again for password then fails. Log just says taking too long and fails.
GRrrrrrrrrrr
P.S. Raspbian on same RPI3b+ no problem with any connection 2.4 or 5ghz - so I am at a loss
After much digging and playing _ good job its high summer - I found the problem.
All my wifi ap/routers work great with every piece of kit I have in their std set up.
Ubuntu mat 18.04 on RPI3b+ does not like GB Wifi settings and no matter how many times I changed this to GB it reverts back to global and does not work on the 5ghz band.
So changing my routers/Ap's 5ghz settings to work on a set channel and band width - the Ubuntu Mate 18.04.2 works - this has got to be a BUG.
RPI-CONFIG on Ubuntu does not give you the option to change the WiFi Country however on Raspbian RPI-CONFIG you can change the WiFi country - how annoying. So if you are unlucky enough to have this problem check you AP/Router settings and change to a channel and band that is supported by 18.04.2 on RPI3b+
I am going to check if there is a setting in the config boot files.
I have been trying to get 5Ghz Wifi to work on my Pi3 B+ running lUbuntu, still no luck. But I did find this bit of information that could help you make the US region setting persistent.
/etc/default/crda