I am having the same issue. I do a daily livestream on twitch and have had no issues for the last several months. I downloaded the new version of OBS and attempted to run my stream today and it completely froze within 5 minutes and then the system completely froze. I could still hear audio but everything else was frozen and stream was no longer broadcasting. I gave the system time to recover itself however I had no luck with that. I attempted to launch Task Manager, however the PC was frozen to the extent that Task Manager could not be launched. After trouble shooting for a moment hoping to find a solution to the problem, I was left with no other choice but to do a forced restart. At the time of the initial freeze and crash I was running NVIDIA drivers 497.29.
Due to the crash I decided I would attempt to update my NVIDIA drivers to 511.79 (which turned out to be a big mistake). I then tried to run my stream 2 additional times, both resulting in the same problem with the PC freezing and requiring a force restart. The second 2 times the issue happened, it happened within 1 minute of starting the stream.
At this point, I took to the discord support page and saw where 511.79 drivers were causing problems with OBS so I rolled my drivers back.
Even after all of this I am still having the same problem.