See if this helps - https://support.mozilla.org/en-US/kb/recover-user-data-missing-after-thunderbird-update

In my case some of the Local folders contents not displaying other local folders display all mails correctly, Like First user will complain some of my local folders mail not opening we will see the problem that yes they are opening blank now we will try to troubleshoot and after troubleshooting(mentioned earlier ) those mails which were opening blank will disappear. Lots of user is facing this issue and we are loosing important data. I ll try your mentioned troubleshooting steps and will update soon.

I tried mentioned method above, Issue not resolved.

i took a case in which local folder containts 8626 mails and i tried to split it in 500 mails per each subfolder and then tried to repair the folder but issue is same. folders first shows 500 messages in one folder then i tried to access some mails from it which opens blank then i tried to repair the same folder and then only 2 mails/ messages remains in the folder.

What OS? Which version of Thunderbird? If Windows, what anti-virus software? Do you have backups of your Thunderbird profile folder? Where are is the profile located - on local disk, or on a network drive?

OS: Windows-10 22H2 x64 Thunderbird Version:- 115 and 128 Antivirus:- Seqrite Endpoint Security 18.00 x64 No Profile folder backup Profile located in C Drive .

Thunderbird Version:- 115 and 128

What version exactly, particularly for the 128.* series?

Is the problem happening with v115.*, or v128.*, or both?

Antivirus:- Seqrite Endpoint Security 18.00 x64

Anti-virus software often causes problems with Thunderbird mail files. I'm not familiar with Seqrite at all. However, these are some generic suggestions to avoid problems with anti-virus software.

Create an exception in your anti-virus software for the Thunderbird profile folder, so that the anti-virus real-time scanner will not scan it. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data#w_how-to-find-your-profile

Don't let your anti-virus software scan incoming and outgoing messages.

Don't let your anti-virus software scan attachments.

Don't let your anti-virus software intercept your secure connection to the server.

Remove any add-ons your anti-virus software may have installed in Thunderbird.

Keep it working. https://kb.mozillazine.org/Keep_it_working_-_Thunderbird

And last but not least, backup your Thunderbird profile on a regular basis. https://support.mozilla.org/kb/profiles-where-thunderbird-stores-user-data#w_backing-up-a-profile

write now i am trying with 115.9.0 (x64 bit) and 128.0.1 esr (32-bit).

we already disabled E-Mail scanning since last 4 years in Seqrite.

is threre any official tool available to recover mails?? is there any limit of Local folder that one folder can contain up to this much GB only ??

write now i am trying with 115.9.0 (x64 bit) and 128.0.1 esr (32-bit).

You didn't tell whether the problem happens with both, 115.9.0, and 128.0.1.

When v128 was released initially it had a nasty problem with corrupting mail files when compacting folders of IMAP accounts. Perhaps this did affect the Local Folders account as well. In most cases the corruption could be fixed by repairing folders. For details see https://bugzilla.mozilla.org/show_bug.cgi?id=1890230

These problems have been largely fixed in the current esr version (128.6.1). Why you're still on version 128.0.1 I don't know.

is threre any official tool available to recover mails?

Repairing folders is your best bet. By now Thunderbird does that automatically if it detects corruption.

we tried to repair folder does not work, we tried renaming .msf does not work.

Repairing folders, and deleting or renaming .msf files does essentially the same thing. There is no point in doing both.

is there any limit of Local folder that one folder can contain up to this much GB only ??

I'm not aware of a hard limit in terms of folder size. Also see https://kb.mozillazine.org/Limits_-_Thunderbird#Folders_and_messages

Issue not resolved....

installed Thunderbird 128.6.0esr(64-bit) in system which was having the issue and tried to repair the folder and noticed that earlier folder was showing total 8626 messages and after repairing folder its showing only 6098 messages, all these mails disappeared, i have already backed up localfolder so still i have the original source, can anyone help...????