all those nstmp folders (files in the file system) indicate your access to the drive is being interrupted and compacts, instead of completing are making copies of data and failing. This is most frequently caused by anti virus product that scan the profile folder while it is in use. I suggest an exception for the Thunderbird profile folder in that product.

So what processes to you have that would be interacting with those folders (other that anti virus which is probably the problem). My goto is always anti virus as it is almost ubiquitous in Windows, but other recent things like folks setting the folder to sync to the cloud are also causes.

Is you google account showing odd folders in Thunderbird like nstmp and sent-1 instead of sent? Or even both!

I have the sent-1 folder. I do have 7 email addresses in thunderbird on this computer.