The default behavior of CMD-Tab is being overwritten by BetterTouchTool so that it switches immediately to the next application instead of showing the switcher. This is deeply confusing. I don't have any shortcuts for "Application Switcher" and adding one manually didn't fix it. For now I'll have to stick with BetterSnapTool until this is fixed.
I have not seen such an issue before (and it works fine here).
Are you sure you haven't accidentally added a cmd+tab shortcut in the keyboard section in BTT?