I don’t have such a source, but the Cybersecurity community throw accusations around easily, and are loathe to ever bless any software as completely innocent - which is a good thing.
When the accusations stop, the issue has either been addressed (typical outcome), or the product owner was written off by the Cybersecurity community as a lost cause (rare, but it happens).
I had a hard time choosing a link. Searching GitHub for “F-Droid” reveals a long convoluted back-and-forth about meeting F-Droid’s requirements for reproducible builds. Signal is not, as of earlier today, listed on F-Droid.
F-Droid’s reproducibility rules are meant to cut out the kind of shenanigans that would be necessary to hide a back door in the binaries.
Again, this isn’t proof. But it’s beyond fishy for an open source security tool.
Edit: And Signal’s official statements on the topic are always reasonable - but kind of bullshit.
Reasonable in that I alwould absolutely accept that answer, if it were the first time that Signal rejected a contribution to add it to F-Droid.
Bullshit in that it’s been a long time, lots of folks have volunteered to help, and Signal still isn’t available on F-Droid.