When I replaced the battery on my 2013 RT (similar battery/charge set-up to your ST

) all the wriggling & movement of the Earth lead at the battery end caused the terminal on other end of that strap, which just happens to also be the main Earth for the DPS, to partly detach from the cable, and as a result, I had some worrying DPS issues rear their ugly head on cornering. :yikes:
After checking just about everything else, I eventually removed the LH Front Wheel and took a look at the Earth point behind the battery under/alongside the DPS where it mounts onto the frame deep inside that LH side 'tunnel' behind the wheel. I was initially just looking to make sure the Earth had a clean connection onto the frame, but as soon as I moved the cable, it was clear the cable & the terminal that bolts onto the frame weren't quite moving together, and that the 'soldered terminal' wasn't really making a good connection onto the cable
OR onto the frame! :shocked:
A bit of judicious application of heat (via a biiig Soldering iron!

) and some solder saw the cable & terminal rejoined as they should've been, and some wet-&-dry sandpaper, a star-washer, & a socket sorted the 'good, clean, & tight connection to the frame' bit and my DPS woes were over!

hyea: Mind you, it wasn't easy reaching in there to do it all, at what was effectively 'full reach', but needs must, and there's a fair amount of room in there for large hands, so I didn't leak too much claret over everything.
Might be worth you having a look in there?! And maybe checking all the Earth Terminals again, including the one on the battery?? :dontknow: