You're interested in Reproducible Builds for Android apps? We've just updated our Wiki on those:
gitlab.com/IzzyOnDroid/repo/-/…
There are new pages for setting up build recipes, and debugging/fixing RBs – which should help you when running your own builder. Which you btw can set up on your Linux machine within 5 minutes using the scripts provided at codeberg.org/IzzyOnDroid/rbuil… 
Developers also find pages there on making/keeping their apps RB.
