The system was vented to  make clearance on the waterlines as a very small continuous discharge was observed.

The inspection revealed some marks on the HS water line (sideview photo). From the the bottom and from real close (zoom and backview photo) the marks are quite noticeable with shinny copper in the middle and dark circles around.

The GND line is routed in such a way that sits on top of the ion gauge chamber (gnd-ig1) this could explain why the vacuum had small oscillation during the current limited events.

Moreover, the GND line has the steerer cables tied to it, this could explain why one of the steerers got affected after the sparks.

Also, the GND line is in contact with a dark grime that goes all the way into the first skimmer (gnd-quad). I think the grime observed inside the test stand might have become conductive, or if this is trace from a previous flashover, this  is good path to flash again.

The EE and the plasma electrode were removed and they show signs of buildup. Cleaned and reinstalled