Root checkers fail to complete on my now non-rooted device

In an effort to get Netflix to run, I removed both Magisk and SuperSU from my Nexus 10 tablet running Omnicron Marshmallow and also flashed boot.img and reinstalled Netflix. It worked! A by-product of this is that, when I run any root checker app, it just hangs after the 'go' button is pressed. My intention is to reactivate root once Netflix and the rest of the system is happily running. Something is wrong in there. Any idea what it is and how I can clean it up? It's been a long business with multiple reloads restarts and fiddling about and I don't want to repeat it all unnecessarily...