Can't launch roms w vice_x128_libretro.dll core through command lines

I’ve been enjoying the VICE x64 core with retroarch, and I’m able to successfully launch games and multi-disk flipfiles with it using cmd lines. However, I can’t launch any game using the vice_x128_libretro.dll core except within Retroarch itself using its browser. My goal is to play the C128 version of Ultima V with enhanced music but this will be impossible unless I can use cmd lines and flipfiles but it just won’t boot, unlike VICE x64 which works beautifully. Here’s my syntax:

“H:\Emulators\RetroArch 1.7.6\retroarch.exe” -v -L “cores/vice_x128_libretro.dll” “x64 -autostart H:\ISOS&R~1\COMMOD~1\UL261F~1.D64”

Is the core buggy? I’m using the latest version.