after plug-ins upgrade PsE no longer launches

After I upgraded my plug-ins (DxO Nik Collection; from version 6.12 to 6.13) I can no longer launch PsE (Photoshop Elements, i.e. version 21 for Mac). When I try to do so, I just get a dialog box (on top of the "splash screen") stating that "There are additional or changed plug-ins or Locales folders that weren't installed by Adobe. Do you want to load these additional or changed plugins?" ...but when I choose the [Yes] option the application just seems to quit the loading process alltogether, exactly at the point where the splash screen text reads "adding extension... Multiprocessor Support".

However, the application will still launch, providing I select the [No] option in the dialog.

I expect that the regular drill applies (clean out and reinstall everything). But since my workflow involves several interlinked tools (PsE and Nik Collection), the administrative costs of doing so – perhaps even without any success – bothers me a bit. Ideas, anyone?