I have the same issue. Dont know why and how to fix it, but: even if i wait for ~1min. OBS comes back. Its most of the Time if i hit "Start Preview" "Stop Preview" or even Stream or Record. Just wait.
If nothing happen, and OBS cant get killed from the Taskmanager, re-log on to Windows, dont reboot, just re-log. Not the best Solution, but will work.