Thunderbird 115.5 mbox files do not read corretly

Linux Mint 21.2 Cinnamon
Thunderbird 115.5.0

After update to Thunderbird 115 I am having multiple email problems.
This problem is TB shows ONE 7.7MB email in a folder

When looking at the mbox file with a text editor, the file contains numerous emails.

I copied the mbox file to another folder and restarted TB ,
TB still shows ONE email with a size of 7.7 MB

After numerous attempts to get TB to read the file I copied the file to my VBox instance of Win10, and used mbox viewer to view the mbox file, and all the emails are visable as emails.

Moved the mbox file I read successfully with mbox viewer, into TB,
and TB still shows ONE email and the 7.7mb size…

Any Ideas ???

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