Bug Report switching between frame rates has a strange side effect

[BK-Morpheus]

Some times my OBS preview window shows some stuttering (Destiny 2 via window_capture, as the anti-cheat does not allow game_capture hook), which is also present, when I then press record and check the footage (but no dropped/lagged/skipped frames in the log file).

I noticed that the preview (and recording) is getting smooth as soon as I go to OBS settings>video and swap down to 10/20/30 fps (some low setting, it doesn't matter which one) apply and then set it back to 60fps and apply again.
Instant smooth preview and recording.

Any Idea why this happens?

System:
R1700x
16GB RAM
GTX1070
Win10 x64 home (v1709)

 

[BK-Morpheus]

That "fix" only works for a random time period (often between 15 and 30 minutes), than there will be stutter for ~4minutes and than it goes back to smooth footage.
Log shows nothing special:

23:11:06.332: Output 'adv_file_output': stopping
23:11:06.332: Output 'adv_file_output': Total frames output: 93800
23:11:06.332: Output 'adv_file_output': Total drawn frames: 93855
23:11:06.332: ==== Recording Stop ================================================

This does not occur with NVENC, just with x264 (no matter if ultrafast or fast preset, as CPU load and GPU headroom is not the limiting factor).
I try to deal with this annoying behavior since month, but nothing (other than NVENC with worse quality) helps.
Can't even find decent google hits when searching for this problem, as most hits are simply related to pretty basic errors (no ingame fps cap = GPU overload or people who are overloading their CPU or whose system is overheating and throttling).