Substratum themes not applying (6P, DU12.1) as pretty much stated above, I have the problem of Substratum themes not applying on my Nexus6P using DirtyUnicorns 12.1 (latest version).

I can choose an installed theme in substratum, choose all the settings I want and hit compile - that's all going well. Substratum tells me it compiled everything correctly, then, when applying, it restarts the SystemUI and boom - nothing. Nothing has changed and when I check back in the Substratum app, it neither lists the theme as compiled nor as applied.

This happens for all themes, I've tried a dozen or two.
It's extremely sad, as themability is THE reason for me of owning an Android device with custom ROM.

Info about DU: AFAIK, DU12.1 has native built-in support for OMS.

Any help would be greatly appreciated :)
Switching off PlayProtect (apperently there is some kind of issue with the recent version of Play Service) and switching on Firebase did the trick.