When activating my /e/ installation on my test device, I had problems with initial registration of Signal.
The cause seems to be, that there are some problems between Signal and MicroG:
Can be solved quite easy by deactivation of MicroG (via Settings->Apps) during Signal-Regsitration.
Afterwards, it can be enabled again.
As both applications are shipped by default, this should be solved for 1.0 release.
Thanks & Regards,