What I believe, Chris_K is saying is that the Affinity Photo beta versions are exploiting changes made in OS X. The fact that Nik plug-ins behave differently under Affinity Photo beta code could very well be related to compatibility issues between Google (DXO) and OS X.
I'm experiencing the same issues, where the Nik Collection behaves correctly with Affinity Photo 1.6.7, but with Affinity Photo Beta 1.7, several of the plug-ins display the "Updating Fonts" window and requires a Force Quit to recover. In my case, this is using High Sierra, as I've not yet implemented Mojave.
It might be as simple as recompiling the Nik Collection using the latest Apple OSX macros, for lack of more accurate terminology. Which, is probably not going to happen with the free Google Nik Collection. If in fact, it's a defect in Nik code, I wouldn't expect Serif to regress Affinity Photo to accommodate obsolete program code. From what I see, Serif has taken this report for further investigation.