Normally you use Signal to send encrypted Signal messages. But you have always a receiver in your buddy list who is not a Signal user. And because of you don’t want to use Whatsup (he still calls the most cool software) you can only send him an old fashioned SMS message.
OK, Signal does this as well without circumstances. Mostly.
 But from time to time Signal hangs and turns the wheel and doesn’t end sending this damned text message. You can close Signal and reopen it, you can even reboot the entire device, Signal doesn’t come to an end sending this SMS message. And it isn’t just a display problem or similar, the message remains really unsent.
The user must solve this situation manually. You must go into the global settings, search for Signal, terminate it and clear the cache. When you then open Signal the next time the message has probably already been sent. And when you now send further SMS messages it will again work very well for a while. Goto 
Note: Sending encrypted messages is never affected by this, only sending of SMS messages.
Does anybody know this? What’s the reason?