The controller runs out of memory., and sacrifices GUI first. a system runing auto, close to interference or cycling in and out, and or have unsaved settings, increases memory load... Prefetch, buzzers, displays, etc consume the available memory... etc.. The latest firmware included an assist for that, obviously hasn't solved it. I've had a few situations with that... one of the first things that helped me on my systems was accessing them in from WAN rather than LAN... go figure...Some of us who run multiple systems, on some browsers, may have a 'cache read' problem, since the files in browser from each system are often same... css, etc... I've suspected that running several systems with very heavy system activity... also note it more frequently when the Wonderful World Wide Web causesslow data transmissions to servers... once the real time 'stroke' display' on the maps hits >6 seconds, and I've got a lot of activity on my controllers, I can almost predict a 'fault' in GUI display... not always, however....