In NTSC, the VIC-20 core is no longer functioning correctly. Many games lock up when they shouldn't.
Simple illustration: Dig Dug cartridge. Although the code is NTSC, it locks up in NTSC fairly quickly after booting up. It functions well in PAL.
Somewhere there's a timing problem.
VIC20_20200504.rbf is the latest version that doesn't do this. It does, however, suffer from sound distortion.