thunderbird stuck with 'Status: Creating mail message...'
Solution 1:
Yes, it appears to be this bug: #687 Enigmail hanging on send - Thunderbird 52.1.1
Work-around
One suggested work-around (confirmed by multiple bug report commentators) is to kill all GPG processes,
killall gpg gpg2
and try again.
Beta-version with fix
You can also install the pre-release version 1.9.8-a3 of Enigmail that's supposed to contain a fix.