Hello,
That sounds super strange. Note that there was no recent update, last version was released 2 months ago (2.2.2026).
The "Old Firefox Data" would appear only if Firefox was completely reset, but then all your extensions would be gone.
If my extension was still installed, but data were gone, then I would guess something has deleted it's contents.
Did you by any chance used "Clear cookies and site data" on the dials page? :)
Or maybe some external tool like CCleaner?

In any case, it may be worth checking the "History / backups" in the main menu on the dials page.
It may contain more recent backup, more info here:
https://github.com/fastaddons/GroupSpeedDial/wiki/Recovery-of-your-dials,-how-are-dials-stored-and-how-to-make-a-backup#recovery-option---history--backups

Best Regards,
Juraj Mäsiar