Allright, I’ll expand 
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No. It’s actually impossible, there are thousand+ apps
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It should. So please (a) be more specific: which app is it? (b) search relevant resources, 1st off https://gitlab.com/fdroid/fdroiddata/issues/
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Discussed many times. The last info is https://forum.f-droid.org/t/steetcomplete-successful-build-but-newest-version-does-not-show-up/3302/2
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No, those are mainly because of the MD5 signature. As wrote 1st turn off the Archive repo.