System- core i7 4790, nvidia GTX 970, 16gb RAM, ubuntu linux.

Prior to an update everything was fine.
After running a software update my distro shows itself as being version 20.04 although I didn't specifically ask for that,
(lsb\_release -d: "Description: Ubuntu Focal Fossa (development branch")

I saw my cpu periodically spiking even doing nothing, and using 'top' found the guilty processes were Xorg, "nv\_queue". Disabling the nvidia driver (going back to an opensource driver) removed this spiking, but obviously leaves me unable to fully use the video card.

I tried going back driver versions - but could only go back as far as version 390, and the problem still happened.

Does anyone know if this is a broad problem with the development branch or something. 
I'm about to try doing a fresh install on another drive (I guess it might specifically be the interaction of the driver and something specific to the latest linux install). 
Maybe there are settings that can be tweaked to alleviate it?
I've seen alot of talk of stuttering with nvidia drivers elsewhere (referencing earlier versions of the driver and ubuntu)