First post here – complete WordPress newbie. I hHad the same problem with the Visual button disappearing on upgrade from 3.7.4 to 4.2.2. In another browser tab, I went to Personal Options and the Visual button was not disabled. So I disabled it and saved the option, returned to my edited page again (unchanged), went back to options and undisabled it and saved, returned to my edited page and it was back.
Although not entirely a cache problem, I suspect that was part of it. Also, having more than one WordPress tab open could cause cache problems.