Been having this issue for the last few weeks.
Whenever I stream I would have moments where my stream would lag down bad, it was kind of random, but more action tended to get worse. Prior to this I had no problem with the settings I had.
I had used a program called facerig in conjunction with vcam, but that is where the lag started. I removed the facerig program and deleted the drivers for it, still had same issue. I then deleted vcam and reinstalled the latest version and the issue persisted.
I tested on both Stream Labs OBS and on Xsplit Gamecaster. Gamecaster had only slightly less lag, (5%<) barely noticable. I made sure my gpu drivers were up to date, installed a clean one to be on safe side. Still same issue. shows many dropped frames.
I isolated it to Vcam being the cause, by closing out of vcam and not having it running, I tried it on both SLOBS and Gamecaster without camera connected (no problems) and again with camera connected but using the standard webcam (no problems) and not vcam.
Confirmed the lag starts with vcam by starting a new stream with vcam active and set for camera.
My Camera is a c920 and my pc specs are high end, so I know it is nothing on that area.
CPU Ryzen 3700x
Nvidia 2080 Super
vcam: 2.3.2105.2001 Driver 1.0.2103.1501