Please be cautious when using third-party tools and software, as they may have compatibility issues or risks associated with them.
The PS2’s USB ports run at 12 Mbps (max theoretical speed). In reality, you get about 1.5 MB/s transfer. If a game's data is scattered (fragmented), the laser-less drive has to "seek," causing stutter.
If you are committed to playing PS2 games via USB, this is the gold standard.
This is usually due to a corrupted ul.cfg file. Use the "Utils" > "Recover List" function in USBUtil to rebuild the index.