I feel for your situation. 0 Bytes is potentially total loss, its effectively corruption.
Perhaps your only hope is if you had a backup, manual or automatic. But you are possibly “behind the eight ball” / at a disadvantage using the older solutions because since we moved on from the original TiddlyFox there are a much richer set of solutions, often with backups built in.
Check there is no backup.
Check your browser has any “local storage” remnants.
If this means a great loss to you, As you say, be carful and see if you can find a temp file before you make too many changes on your storage. I have lost and never found things and this will not necessarily have any results.
There is a chance if you find the file located on disk that the bytes that follow are the old content. With a direct to disk editor (dont install it, run from USB)
5.2.0 introduces some architectural changes that may not survive the older savers.