This defect has been there for a while where on occasion the APK will download but the install (with privileged extension on a rooted system) will fail with a message like:
E/AppDetails2( 1073): install aborted with errorMessage: /storage/emulated/0/Android/data/org.fdroid.fdroid/cache/apks/example.com–1/apk-name.apk failed to verify!
Repeated attempts at download/install resolve the problem on its own.
There appears to be a race-condition in the installation process which copies the APK from one location to another during the install, clearly something isn’t always ready for the Privileged Extension to pick it up. I can give it a shot at fixing it and submitting a patch for review but this part of the code is older and slightly convoluted so if the original maintainer is willing to have a second look before me that would be great. The good thing is that on my system I can reproduce the bug fairly easily.
Let me know either way!