Disclaimer: I consider myself somewhat of a handyman at home, but this one's got me stumped.

TLDR: I switched out halogen 12V G4 lamps for LED ones and they only flicker once when switched on. 2 LED 1 halogen works for some reason.

I wanted to replace all three halogen 12V lamps with (what I thought) fitting G4, as one of them burned through. So I went on replacing them one by one, testing each before closing the lid again. The first one worked perfectly, as did the second one, so I happily started replacing the third, already considering myself lucky I got off so easy with a quick task.

Nothing was further from the truth. After replacing the third lamp, I switched on the lights and they turned on again! You might think, "No problem there right?" and you'd be right about that, if only they stayed on. Much to my dismay, after only a split second they switch off again.

Now, I called myself somewhat of a handyman at the start of this post, so this is my time to shine. I try the old halogen again, and the lights stay on. So I switch back to the LED, but alas, the bad results remain. I try turning the LED so the pins connect the other way around, and as expected no improving results.

I also searched the internet, but this problem is kinda hard to specifically search for if you don't have the words for it, so that's why I resort to asking the most helpful (hopefully) bunch of electricians.

What is going wrong here? I would really like to understand.

12V Halogen to LED