If I bring up the app switcher using CMD + TAB and then quit an app using CMD + Q it will only allow me to quit that one app and then it gets stuck. I have to invoke the app switcher again to be able to quit another app.

As a side note just as an observation; in Mojave this doesn't respect SQA and quits the app instantly but I won't comment either way as to whether it should or shouldn't as I don't have an opinion on that.