My WLM 2012 is running on my PC-Windows 10 Build 1909.  I have over 35 gigabytes of email messages,mostly in Storage Folders to which I sometimes access and add.

Yesterday,while trying to copy and paste from a secure website,I received a fleeting popup that stated " your WLM data has been lost." Apparently,i had overloaded my beloved WLM!!  I then saw that all the messages in my Inbox,Sent,Draft,Junk,Delete folders had been [properly]moved to newly-created Storage folders ! The data of these messages are all readable,etc.,and have full Properties in the appropriate folders found in C:\Users\name\AppData\Local\Microsoft\Windows Live Mail.

However,here's the real problem: The vast bulk of my messages's Subject headings in my WLM Storage folders ARE present but the original content unavailable to read as apparently proper communication with an uncorrupted (?) Mail.MSMessageStore (?) has been lost (?) My Mail.MSMessageStore currently has 462 MB of data in its Properties. (FYI-In a WLM backup i have saved from August 2020,496 MBs were then present in my Mail.MSMessageStore.Is this change significant?) 

Though i can read the correct Subject headings when i open these messages in their Storage folders in WLM,all the messages in a subfolder have the same content when opened.And the content states "Empty" when i look at the corresponding subfolder in C:\Users\name\AppData\Local\Microsoft\Windows Live Mail with Properties of "zero."

I did copy everything-(Properties STILL STATES IT HAS THE CORRECT NUMBER of GIGABYTES!!) now present in C:\Users\name\AppData\Local\Microsoft\Windows Live Mail into another SATA-box connected hard-drive disc before attempting any further steps.The properties of the affected subfolders are the same here as in the "C" drive but no further steps have been taken yet as i await guidance if available.

Thank you for your kind attention.