Did you select the correct account in the Filters for: box at the top of the Tools/Message Filters window? Filters are defined per account.

Yes, I did select the correct account in the Filters for: box/drop down. I should have stated that in my original post. I just went back and double checked it and the filter that I modified is still not present in the list of filters that run on my mail in box. I did enable the Filter Log this morning and the remaining filters appear to be working properly.

For your information I have 179 items in my Message Filters list. I also have about the same (probably a few more) number of Local Folders as I usually assign 1 local folder to 1 message filter.

I can't say why it's not showing in the filter list, but if you look at the msgFilterRules.dat file in a text editor, does it appear there? The dat file is in the subfolder of the Mail or ImapMail subfolder of the profile folder for each account. Help/Troubleshooting Information, and click Open Folder to open the profile folder.

Found the msgFilterRules.dat file and opened with Notepad and could not locate the missing filter. Also I did not see a remnant/fragment of a filter or any evidence that the file might be corrupted.

I am going to recreate the filter entry and hope for the best.

@sfhowes Thanks for your assistance. I learned something that may help down the line.