A cautionary tale about using Flask in debug mode with Python Threads

Let me just say I did hours of "debugging" just to find that if you use Flask in debug mode and are using Python Threads, the threads execute at least twice and sometimes 3 times.

I was creating a queue for email being sent to allow for one process to be sending the email and I was usually getting 2 but sometimes 1 and sometimes 3. I finally found the correct research query to determine that the issue was FLASK_DEBUG=true isn't compatible with running threads in an asynchronous manner. It didn't matter what I did to try to avoid the problem, there was always the potential for multiple emails.

Just wanted to share here so you can avoid wasted hours on trying to "debug" a problem in the code.