This morning, my wife's Thunderbird messages on version 102.11.2 were blank. They were IMAP messages on gmail, and a quick check showed the were not blank on the server. I tried deleting the entire gmail folder set from the IMAP mail directory, but that only made it worse. So I loaded my wife's profile from a backup. It solved the problem, but for how long? Another person with a similar issue previously noted that another symptom was a vast increase in storage requirements for the profile, and I saw that the profile was more than three times the size it used to be. There were a series of files named NSTMP in the gmail profile that aren't present on my profile. I deleted them from my wife's profile and recovered the storage, without changing the performance. I suspect the profile became corrupt and the corruption resulted in generation of multiple NSTMP files, and eventually started wiping out message content as well. Because I think the profile I restored was likely corrupt, I am guessing this problem will recur, unless someone can tell me how to fix it for good.

I'm running Windows 7 with all updates current as of the time MS stopped supporting it.