Hello, I've had the same problem, and found the solution by chance.
Deleting retroarchcustom.cfg makes game launch fast again.
If I save configuration from retroarch's menus, it creates a new 97Kb retroarchcustom.cfg...
And everything is lauching slow again...
There's something in this big retroarchcustom.cfg that makes it launch slow.
I didn't take time to analyse the full retroarchcustom.cfg, but there's a big difference with retroarchcustom.cfg.origin : input_joypad_driver is set to "sdl2" before saving. Saving from retroarch changes input_joypad_driver to "udev"...
