Simply Static fails

I’m trying to use Simply Static but it fails and doesn’t do anything, no spinning, no output box, no debugging logs. The diagnostics are all OK and the “Checking if WordPress can make requests to itself” returns 200 which I assume is good. The directory I have selected to write to is Unix permissions 775. I have tried changing delivery methods, the location of the local files directory, relative vs offline, delete temp files, etc. Same result. What else can I try?