XPS 8950, SupportAssist won't load

Well - that's not quite correct. SA 3.14 does load as a process, I just get no on-screen indication or options,  and there's nothing in taskbar hidden items. If I start the app, there's a quick flash on screen - too quick to see what it is - which goes away,  then a brief flurry of activity in Task Manager and then SupportAssistAgent.exe just sits there occupying 170MB of memory. I can't open any related window. I tried to repair it in Settings - same reaction. Tried to download the latest version and reinstall over the top of my existing app but - "you already have the latest version". So. I can run tests and download updates from the website - is it worth spending any more time on this? TIA for any advice!