Only on mobile phones, and some VoIP systems. The PSTN won’t understand + (I’m not actually sure that the mobile network does either; the phone may actually change it into type of number = international, and only send the the digits starting at 35.)
You’ll need to show the match patterns for the outgoing route to see why numbers starting in + are not being sent to Twilio.
This may be helpful, although you may or may not agree with some of the policies proposed: