I've been using After Effects CC 2015 for a little while now and haven't had too many problems. However, I recently had some issues with CC on my machine, so did a clean re-install of everything, and in doing so I've obviously been bumped up to the latest AE 13.7 version.
I work a lot with the rotobrush, but somehow between the last version and the current one I'm using, an issue has arisen. Every time I do a stroke with the rotobrush and release the mouse, the footage in the viewer disappears momentarily to the grey of the background, then comes back in. It's very brief, and the rotobrush seems to work at the same speed as before etc, only this constant screen blip is extremely irritating, makes it harder to work and is also giving me headaches (literally!). This never happened before. Any ideas?
I'm not sure the exact build number, but basically before the re-install when things worked fine it was CC 2015, the version with the load screen that had a purple vista with a sunset in the background and sorta white light pyramids. The version I have now (problematic) is the 2015.2 release, 18.104.22.168; the current version. Got a sorta man/tree composite load screen going on.
Windows 10 Pro
Intel Core i7-4770k CPU
NVIDIA GeForce GTX 760
I'd recommend filing a bug report so Adobe knows it's an issue. They've been trying to squash bugs related to the new previewing architecture and it's possible that, when they fixe done of them, it caused another one that you're running into.
Here's the page for filing a report: http://www.adobe.com/products/wishform.html