They've said that they release the source code after it's running in production:
sorry the source for one of our services was so far behind. We often don't push source until we release things, and there were a few overlapping releases that happened in that period which made it awkward to push at any moment and put us behind. Additionally, we've seen a large increase in spam, and a reluctance to immediately publish the exact anti-spam measures we were responding with to a place where spammers could immediately see them combined with the above to cause this extreme delay.
Untrue. Stop spreading FUD: https://github.com/signalapp/Signal-Server
There's a grain of truth in the claim: We don't know for sure if the original open source version is actually running on the server.
Isn't that true of all server side FOSS?
Yes. We just have to trust them. Or selfhost, which I'm doing with almost everything.
They've said that they release the source code after it's running in production:
https://github.com/signalapp/Signal-Android/issues/11101#issuecomment-815400676
In that case: They started publishing code AGAIN.
The server soft has been available, then not, and apparently now again.