I have this same problem, having lived with it for months I'm finally trying to get it sorted.
My PC is a custom build, about a year old. i7, 16GM RAM, SSD, etc. ASUS motherboard. Using Webroot AV, Windows 10 Pro build 1709, Firefox Quantum.
So far I have tried 'allowing' both Firefox and Task Manager in Webroot, both Identity Protection and Block/Allow Files
None of the above steps have made a difference, and each time I have to kill Task Manager via externally accessing my cmd line in order to regain control of my PC. Previously I had to cold reset each time this happened which I hate having to do.
From this thread it seems different things are working for different people but there's no guaranteed fix or workaround (other than ditching Task Manager or Webroot for alternatives).
I'll raise a ticket directly with Webroot support, I work for an MSP and we have a decent amount of endpoints so hopefully they take this seriously and come up with a fix.
I hope you can find some sort of resolution. I had opened a ticket with Webroot regarding this and was basically told they have had some other reports of this and was advised to disable the Identity Protection or put it into safe mode. Which doesn't seem
to be working for me now.
I've done several different workarounds, and with each one it was resolving the issue for a short period of time.