Peter there are three triggers on the loom that can bring on that light. The left and right brake fluid level sensor cap connections (one redundant dependant on l/h or r/h drive car) plus handbrake connector. All signal wires are black/white and are paralled to a single wire of same colour running to the 9 way Tyco connector (only eight pins used) feeding driver LED warning strip. A short to ground at any point on these wires will trigger the warning. I could be you have found such but a little concerned fault re-appeared even though just once!
You haven't mentioned if you checked the redundant wires to l/h drive position of brake master cylinder. These should be individually insulated and cable tied out of harms way.
Not sure what "PCB" you replaced but the GDI model's (2014 on) employed a sealed BCU, was it just the warning light strip interfacing with the above mentioned connector?
