I had an earlier email loss from July 2014 to November 2014. The emails in a Thunderbird crash just disappeared. I don;t know what happened there either but at least had my "Sent" Folder to help me recover any emails I happened to have responded to, but lost many that I had not replied to to generate a saved copy in my sent folder. I have had 2 critical crashes or corrupt files and seriously concerned after so many years of Thunderbird being so stable. I want to know what happened and also if there is any way to recover.

even double clicking then that opens a new tab is blank.

Possibly there's some sort of corruption. You can try to rebuild the index file of the troubled folder. Right-click the folder - Properties - Repair Folder

In best case this could restore everything to normal. In worst case this could erase messages back to 2009, depending on the state of corruption.

So before doing anything make sure to have a backup of your profile folder. http://kb.mozillazine.org/Thunderbird_:_FAQs_:_Backing_Up_and_Restoring

I have had 2 critical crashes or corrupt files and seriously concerned after so many years of Thunderbird being so stable.

Then you hopefully learned from that and you did create backups on a regular basis.

I want to know what happened ...

The most common reason for corruption is anti-virus software writing to Thunderbird files when it shouldn't.

... and also if there is any way to recover.

There is no guarantee. But if you have a backup then there is no problem.