So... not using Signal because it's based off a conspiracy theory that it's secretly funded by CIA?
Well, let's stop using RSA and encryption because the most used secure crypto algorithms today were created by none other than the NSA!
EDIT: None of the alternatives provided are good alternatives for Signal. Matrix is an extremely complicated protocol that lacks some features compared to normal IM apps (I use Matrix and the experience is quite close to a standard messaging app). XMPP is dead and has a very niche userbase. The others are not suitable for being a daily messaging app.
Signal is a good alternative and while I do agree with some points, they are not bad enough to prevent you from using it (e.g. not having usernames).
That doesn't seem to be the case. From what I read on HN, the dev quit because he thought it didn't make sense to submit CVEs for temporary/wip solutions, and F5 thought otherwise.
So as I see it, the developer quit because he didn't agree that a CVE should be opened for a work-in-progress solution that was live on Nginx.