Might be worth to mention:
I have a i5 2500K (yea it's old but still works, and it should be bottle-necking even quicker then most of the cpu's people have here)
8Gb ram.
Geforce GTX960 driver: 382.05 whql
And i have win 7 64-bit ultimate.
Norton AV
Trying City Skylines as that was reported by someone else.
game runs on 1920*1080 no vsync.
And i record on x264 no rescale @60 fps 2500 bitrate verryfast.
Alt tabbed a lot of times but
could not reproduce the problem.
But i have also have to say that i did not test streaming tbh.
HOWEVER:
I have set my custom x264 options with 'threads=4' (without quotes, it has been long on that setting as it seems to had a bit better preformance years ago with classic)
(my cpu has 4 physical cores)
Not sure if that would help anything but i don't have any problems with recording anything i want.
Sure my cpu and mem is nearly maxed out but hey, it still works with no encoding error.
And i still use webpages, hexchat and mspaint in the background for uploading this photo while still recording.
https://gist.github.com/e903b854292ff0972966d49c762de00f
Edit: added log file and resources overview.
Edit 2: Subnautica also did not give any problems/warnings.