Ok, found the limit (in my case anyway):
Scanning 2307 detected items works
Scanning 2308 or more makes Tiny Launcher crash for me.
I have discovered a new bug, though. It was a bit hard to track down, but here you are:
When the last directory scanned contains exactly 20 entries, the listing only shows one entry for the affected directory. (e.g. 20 slaves in "Z" subfolders)