It may come better across if one first asks if there are any Google Play libraries used, when they are not able to audit the open source code for themselves, and not plain starting out to imply that this is the case, from some possible completely unrelated observation. We really try hard to provide a fully Open Source experience here, that's why an implication of willingly linking against proprietary libraries, even if we state otherwise, is taken rather serious.
Anyway, it'd be great if you can share some more information - i.e., Device, Android Distribution used (and which version) what tool was used for the app extraction, was there anything to be seen before the crash, ...
I just tested the app on an GAPPS free Android-x86 VM (a 8.1 based was the one I could get my hands on the quickest, the others surprisingly all shipped GAPPS), and there it works fine out of the box - didn't need to alter a single thing.
I uploaded a build here: https://lamprecht.org/download/pve/pve-mobile-app/pve-mobile-testbuild.apk (
Maybe you get around to test that.
Running the app on Sailfish OS and it works perfectly.
Please release it on open platforms as F-Droid
Thanks for the great work!