I used recuva to recover a deleted directory and, as the destination SSD was defective, I had to perform the procedure twice. On my third search, the folder no longer appeared in the search results!
Is this a limitation of the free version? Do I have to buy the license to retrieve this folder a third time?
Buying a licence will not do anything different than the free version, other that giving you paid-for access to the support team (for what that's worth).
If you used the same search options/parameters then it should have found the sme things again - unless something had changed on the drive being recovered from.
You say that your first recovery didn't work because it was to a faulty destination drive - you didn't then recover back to the same drive that you were recovering from did you?
That could have over-written what you were trying to recover.
Was there something wrong with that second set that you say you recovered?