If you need any other information regarding this, please ask and I will gladly provide it. As you may imagine, this issue is driving me mad! 
   
 Thank you for any kind of help you can provide to fix this weird issue.

Hi everyone, I've been experiencing weird troubles with some messages. When I click a message in the list to open it, sometimes the message opened shows parts of other unrelated messages, including incomplete content, lines of base64 encoded strings, boundary lines, partial html code, you name it. Looks like sometimes the program just mixes valid headers with parts of other random messages, starting on random lines. Sometimes the message content shows only the final line of the code of another unrelated message (the boundary end). I'm attaching two captures to illustrate the issue. Only one folder is affected (well, unluckily for me, is the INBOX...), so I guess that file is the one broken. I've tried the "repair" option on the affected folder, to no avail. Sometimes looks like the problem is gone, but then another message that was ok before shows up broken. Thunderbird version is 128.1.0esr (64bits), running on Windows 11 Professional (23H2). Profile size is 30 GB, INBOX database file is 16.757.000 KB by now, with 17.445 messages. I'm using IMAP as server, and no message is broken on the server (I've checked them on the webmail service). The machine is using a SSD, NVMe kingston RBUSNS8 239GB, if you want to know... It's ok AFAIK. If you need any other information regarding this, please ask and I will gladly provide it. As you may imagine, this issue is driving me mad! Thank you for any kind of help you can provide to fix this weird issue.