Help: Extremely bizarre behavior of my StingRay Special

Hi,
maybe some of you guys remember my previous posts here about my SRS.
I’ve recently acquired a beautiful StingRay Special 4H in Dropped Copper. After a couple of weeks, I noticed that the signal was randomly going off and back on.

Symptoms:
What I heard when the signal was going off and back on is a peculiar “click”.
That is the active preamp engaging when it detects an electrical signal going in (jack cable inserted with amplifier turned on).
If you unplug the jack cable and then plug it again, you hear that “click”.
If you open the battery box and then close it, you hear the same exact “click”.
That’s because the preamp doesn’t have power anymore and when it comes back, well… it does the usual “click”.
So far so good, right? Bare with me.

Possible cause and solution:
I did some tests at home and unfortunately I couldn’t understand how/why it was happening, so I’ve sent an email to EBMM and after talking with them I shipped my bass to my official local distributor, which also does repairs for EBMM.
They couldn’t identify the problem and they said the bass worked perfectly and didn’t show any problem. They talked to EBMM again and decided to replace the entire motherboard (with preamp, controls and all that stuff).
Well, one thing and another… I got my bass back after almost 3 months. But that’s another story.
Unfortunately, I couldn’t spend enough time with my bass when it came back home because I was traveling for work, but it seemed to work fine with the new replaced parts.
During this lockdown thing I finally got the chance to spend some quality time with it and guess what? It’s happening again!
I must say this is not a rant thread, I just want to solve the problem asap. I’ll contact EBMM via email and complain with them of course, but not here.

So… let’s start excluding the replaced parts. I’m pretty sure it’s not the preamp, the motherboard, or the controls. Everything has been replaced.
I think it’s the output jack, so I started doing some tests with it. A couple of days ago I discovered some important things:
1) Touching/moving the jack cable doesn’t trigger the defect. So the output jack port is not loose, maybe something is happening inside, definitely not outside.
2) If I play sitting, it definitely happens more often.
3) If I tilt the bass forward and rotate it around 90 degrees, I’m able to trigger the defect. The signal goes of (with approximately 1 second of delay) and then back on, and of course it “clicks”. Imagine being on stage and tilt your body forward to reach a pedal in your pedalboard. That causes the problem. Why? I absolutely don’t know.
4) The battery box isn’t the culprit, imho. I tried to put a little spacer inside the battery clip to make the contact tighter in order to prevent a possible loose contact and nothing changed.
5) Angled jack cables seem to trigger the defect more often, but I’m not 100% sure.
5) If I use Proel cables, the problem disappears completely. With all my other jack cables, the problem is always there. Proel cables seem identical to my other cables but I guarantee you they somehow solve the problem. Why? I don’t know.

I think it’s the output jack, but what is happening? This is really strange and annoying. Never experienced something like that.
Please, help me solve this problem. I love that bass and I won’t give up.