I'm with @JoesemM ...
I tried every which way I could think of to find a reference to an "M" having to do with Reconciliation. The only things I can find that should be part of an Acct should be C for Cleared and R for Reconciled.
Thanks for providing a screenshot of your Reconciliation Report, @Bowie
I'm here to share some information about the letter M on your report.
QuickBooks Desktop displays unique symbols to represent the status of your transactions. I've listed them below. These are the symbols that you'll see on the printed reports:
In case you want to learn about the available columns and filters in QuickBooks Desktop (QBDT) reports, I suggest checking out this article: Customize reports in QuickBooks Desktop.
Please leave a comment below if you're referring to something else or if you have any additional questions. I'll be happy to answer them. Have a wonderful day!