SB-28 "Sleep" Problem

I have been using two DSLR camera trap set-ups for quite a while now without much problem. I built the cable harnesses for the flashes myself and recently upgraded a camera body – and now there is a new problem. I will lay it out below:

Trap combinations that work flawlessly:
Nikon D7500 & D810 bodies
Cable harnesses made with JJC camera shoe cords
SB-28 flashes (3-6 depending on the trap set-up)

I recently tried to upgrade one camera body to a Nikon D850 and now the SB-28s will not go to sleep. They seem to wake each other up (when two or more are daisy-chained). Does anyone know what differs in the D850 from the D7500 & D810 bodies, and what might be causing this problem?

Thanks you