the equipment:
Headlight: B&M Lumotec IQ Cyo Premium Senso Plus
Dynamo hub: Shimano Alfine DH-S501
Taillight: not sure, I think it's a Spanninga Pixeo

the setup:
The wires are connected with soldered-on 'banana' connectors pretty well encased in heat shrink tubing with dielectric grease. Where possible, the wires run under the fenders, attached with tubular tire cement and pieces of gorilla glue.

the problem:
The lights stop working for no obvious reason. Sometimes they work, sometimes they don't, and even when I get them working again, I don't know what I did to make them work.

Typical situation: before leaving the house, I pick up the front of the bike and spin the wheel, and both lights work fine. But when I get on the bike, the light starts flickering and then goes out. When I stop and pick up the front wheel and spin it, now the light sometimes works and sometimes it doesn't. I check the connection at the hub (pull it off and push it on again), and now the light works... or maybe it doesn't. Pull apart the banana connectors and put them back together again, repeat the test... and the light works, or maybe it doesn't. If I repeat these steps, sooner or later the light works again, and I get on the bike again, and all is good. Or maybe the light starts to flicker and then it goes out again. After it goes out completely, it may still give a bright flash of light every time I go over a bump, but remain dark when the road is smooth.

This has happened several times over the last month. Several times I've missed my train after losing time futzing with the light. Something similar happened on a couple long rides I did in April; in both cases I got the light working eventually and it worked fine all through the night. But I never did diagnose the problem. After the first such occasion, I replaced the wire and the banana connectors, and thought I had solved the problem; but it recurred.

This morning, after stopping to play with the wires three or four times, on a whim, I tightened the quick release on the front hub. That is, I released the QR (it was not loose), tightened the nut a quarter turn or so, and locked the QR lever down again. I made it really tight this time, so it was hard to push the lever into position.

And this seemed to solve the problem. The light worked all the way to the station, though I had already missed my train.

So, my question is:
Does it make any sense that tightening the QR should solve the problem? What's going on here? What do I need to do, to make this setup reliable?