My Kryptonite U-lock mount to bicycle frame broke inside after couple of years, so I made broken part replacement. Its little different than original (tried to make it last longer while printed in PLA) but fits inside and works, at least for now.

Print horizontal and with supports.
Because part is thin you should try printing with more durable filament than PLA (maybe ABS or PLA+) but I dont have one to try it myself.