Snap maintainer here.
This is due to a DMCA takedown request coming from people representing Signal. Canonical is currently working with Signal to resolve this issue.
There was an initial communication breakdown between me and Canonical due to how the Snapcrafters publisher is structured. Canonical is changing their procedures to make sure this communication breakdown doesn’t happen in the future anymore.
I’ve suggested to Canonical to be more transparent with DMCA takedown requests, similar to how GitHub does it. Last I heard, they were discussing this internally.