Reason: The minimum diameter of castellated holes is 0.6 mm and the minimum distance between two Plated half holes is 0.55 mm.
Suggestion:
A: We suggest you to design the distance for the castellated holes to be 0.6mm and the gap to be 0.55mm.
B: If the gap is only 0.5mm and you can not enlarge it, the board can be made in our high-precision line for production.
For any detail information, you can see the link
https://www.pcbway.jp/pcb_prototype/What_are_Plated_Half_Holes_Castellated_Holes_.html