2 days ago I updated CC. Since then, the Roto brush in AE has been working improperly. In the layer panel, I can't view the whole image I'm working on, that is, I can see my selected areas only against a black, magenta or red background, but not against the original background. Obviously, I can't work this way. A second thing is that, since the update, the Help menu in AE is not working, but that's a minor issue compared to the Roto brush. Oh, I uninstalled and reinstalled the program, and nothing changed. Any help appreciated.
Nobody can tell you anything without proper system info or other technical details like comp settings, footage used etc. This could be a CoDec issue totalyl unrelated to RB or some issue with the new preview functions. Start by checking your preferences and viewer settings and turn off GPU acceleration to test.