Is this an addon that you are using? If so, your best bet is to contact the author.

No, actually go to menu bar, tools and scroll down to "remove duplicates". This has worked in previous versions, I don't use it very often so I can't speak to which version was the last that it did work. Thanks for the input.

Please check addons again. I do not see a 'remove duplicates' on my 115.

David, you are correct! Somewhere along the line I must've installed an add on and forgotten about it. I appreciate the "relentlessness"! lol Thanks again.

Indeed remove duplicates pretty much stopped working thunderbird 115. I see messages which are obvious duplicates which it does not find.

when i change the settings for the addon by severely reducing the number of things it compares (probably to the point of unsafe comparisons) I can SOMETIMES get it to work.

It never remains working for long. Pretty much the next time i use it (after thunderbird restart) it once again does not find obvious duplicates.

before 115 I never had any issues with this addon.