Since updating to macOS Sierra, many apps fail to respond correctly to Command+Tab switching.
For example, if the three most recent apps are any two other apps A and B and C, in the order A B C, Command+Tab from A briefly shows B, and then immediately switches to C.
Examples of B that exhibit this behavior include non-Apple apps (e.g. TextWrangler) as well as Apple apps (e.g. Messenger). Changing at least some apps to full screen causes them to behave correctly.
"Manually" switching by holding Command+Tab and selecting B fails in the same way.