I'm getting this error in the SL beta:
Interface\AddOns\AllTheThings\Settings.lua:37: attempt to call method 'SetBackdrop' (a nil value)

Blizzard changed how frames support backdrops. For reference to this change, see here:
https://www.wowhead.com/news=316954/addons-now-available-for-use-in-shadowlands-beta

We haven't done a release with SL support yet, but you can download in-development version here, it has it fixed.