For the latest version our test script. came to this conclusion:

Results:
appId:          it.airgap.vault
signer:         486381324d8669c80ca9b8c79d383dc972ec284227d65ebfe9e31cad5fd3f342
apkVersionName: 3.3.0
apkVersionCode: 20379
apkHash:        caa4da6ca8fa905e4b25594bebbbcb4bfe030a70178ca65a9b0a60f2651bb316

Diff:
Files /tmp/fromPlay_it.airgap.vault_20379/apktool.yml and /tmp/fromBuild_it.airgap.vault_20379/apktool.yml differ
Files /tmp/fromPlay_it.airgap.vault_20379/original/META-INF/MANIFEST.MF and /tmp/fromBuild_it.airgap.vault_20379/original/META-INF/MANIFEST.MF differ
Only in /tmp/fromPlay_it.airgap.vault_20379/original/META-INF: PAPERS.RSA
Only in /tmp/fromPlay_it.airgap.vault_20379/original/META-INF: PAPERS.SF

Revision, tag (and its signature):
object 453b522dbbe53a603ccbfd01d07bf24f85ad838b
type commit
tag v3.3.0
tagger Andreas Gassmann <a.gassmann@papers.ch> 1595232900 +0200

Version Code: 20379

which is what we expect to see for the verdict: reproducible.

Verdict Explained

Reproducible: The provided Source Code matches the app released on Google Play

The app can be independently verified. If the provider puts your funds at risk on purpose or by accident, security researchers can see this if they care to look. It also means that inside the company engineers can verify that the release manager is releasing the app based on code known to all engineers on the team. A scammer would have to work under the potential eyes of security researchers. He would have to take more effort in hiding any exploit.

"Reproducible" does not mean "verified". There is good reason to believe that security researchers as of today would not detect very blatant backdoors in the public source code before it gets exploited, much less if the attacker takes moderate efforts to hide it.

To understand why some lines of difference are ok and others not one has to consider how app signing works. Android supports currently 3 signing schemes and in version 1 signing the signature is put inside the application file. As the tester must not have the release signing key, those files necessarily are missing or differ from the version on Google Play. The file "apktool.yml" was never part of the app and is generated by the analysis tool "apktool".