Substratum themes not applying (Nexus 6P, Dirty Unicorns 12.1 Oreo)

I have the problem of Substratum themes not applying on my Nexus 6P using Dirty Unicorns 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 owning an Android device with custom ROM. Info about DU: AFAIK, DU 12.1 has native built-in support for OMS.