Getting exclamation "!" sign in email notifications in composer on random locations.
This is actually a known SharePoint issue that has to do with SMTP setup. Here's one of the threads talking about it: https://social.technet.microsoft.com/Forums/en-US/91c383e9-f7a0-4446-b781-302682b3bbb0/sharepoint-2010-workflows-add-random-characters-into-email?forum=SP2016.
And another: https://answers.microsoft.com/en-us/office/forum/office_2013_release-outlook/outlook-2013-adding-random-exclamation-marks-to/86280930-d026-4f91-9819-fc3fc383fb44
There isn't a Winshuttle fix for this but we have seen it most commonly for customers who do not use an Exchange server for their SMTP. Once they switch to an Exchange server (if it is possible), the issue resolves.