Since I upgraded to Thunderbird 78.3.2 (32-bit), any subject line I enter for a mail merge gets completely ignored and messages with blank subject lines are produced. I have tried uninstalling the Mail Merge addon and then re-installing it, all to no avail. Operating system is Widows 10. No other add-ons are installed but Enigmail was installed on the previous major release. Any suggestions as to how to resolve this would be really appreciated.