sometimes drops within a few minutes of logging on, other times may run for an hour or so. Sometimes will eventually reconnect but mostly have to disconnect and reconnect to AP. Sometimes forced to turn off wireless and back on again before it works. occasionally the only way to get network is to reboot.
sometimes after reconnecting the connection remains for sometime, other times it drops almost immediately again
I have tried with both 2.4GHz and 5GHz connections remembered and when one drops the other tries to start but found suggestion that this can cause a problem when wireless flaps between the two so have tried with just one or the other set up. Problem exists on both.
have tried this
sudo add-apt-repository ppa:hanipouspilot/rtlwifi
sudo apt update
sudo apt install rtlwifi-new-dkms
but ended up with no wireless connectivity at all
I am using Kubuntu 16.4 and have had the issue for months. Keep hoping an update will fix but nothing as yet. kernel is 4.4.0-57-generic

oh and not confined to my home wifi either, reproducible on others too

Unfortunately this is definitely a problem somewhere in the underlying software (either driver issue or a bug in NetworkManager). I would start with opening a bug report for NetworkManager where they can help you more than me.

NM bugzilla: https://bugzilla.gnome.org/page.cgi?id=browse.html&product=NetworkManager

(In reply to Jan Grulich from comment #3)
> Unfortunately this is definitely a problem somewhere in the underlying
> software (either driver issue or a bug in NetworkManager). I would start
> with opening a bug report for NetworkManager where they can help you more
> than me.
> 
> NM bugzilla:
> https://bugzilla.gnome.org/page.cgi?id=browse.html&product=NetworkManager

Thank you, I will do that