Thank you very much! Can I buy a new insulator and if so where should I look?
Some mods come with spares, but it is usually more expensive mechs that do that. For a regulated mod, it may be easier to replace the whole 510.
Before going that far I would definitely check all other options like the battery and wire clippings on the rda deck. If the mod still acts the same with a different atomizer, it is probably not an RDA issue. If the RDA is the issue, look for wire scraps hiding on the deck, and check the RDAs 510 pin and insulator (plastic insert under the pin, looks a lot like the insulator in the picture).
There could also be a loose wire somewhere in the mod (I've had this issue with a Pico 75). I've even seen pieces of solder brake free and lodge into inconvenient spots.