I had this(?) recently in prod on two bots at once, web browser suddenly just stopped being visible to BP in the middle of the running process: IE is lauching, but even navigate URL fails. When I tried spying, there was no HTML mode at all - VM reboot solved it, but left me pondering what just happened.
Another dev around the same time had a process that would attach to java app just fine using step-in, but BP hang forever using step-over/control room, despite clear logic inside to fail on repeated exceptions. Worked on my PC, hanged on two others.. not sure now if reboot solved it for them.
Heisenbugs ftw.
It could be some kind of silent OS update that left something in system out of sync until reboot, but since I can't reproduce it, it's hard to tell.
tldr: try reboot first