This is a limitation of the PS2's USB 1.1 ports. Use defragmentation tools like Auslogics Disk Defrag on your USB drive after adding games.

: Modifies, renames, deletes, and recovers damaged ul.cfg game lists.

This article provides everything you need to know about USBUtil v20—its features, legal considerations, how to obtain a clean English version, step-by-step usage instructions, and safer alternatives.