Recent versions of egrep generate warning
I've been following this bug, as this bug has been affecting me, too. One out of every 4-5 messages sends would hang on "creating message." Happily, I was able to send over 20 test messages without any problems after installing https://enigmail.net/download/beta/enigmail-1.9.8-a4.xpi. FYI, I believe it's also solved a recurring problem I've been having where messages with good signatures (e.g., messages I send to myself) are not recognized as such.