This could of course be an issue with the adapter, rather than the SD itself, especially if you managed to get one of the atomisers working, and if the attys work on another
device.
Really the only advice anyone can give you is to contact the Supplier you bought the MKII from, and discuss it with them.
If an item proves faulty in a very short time, including an atty, and as you say the first one gave out within hours, then its a matter of reporting it to the Supplier, not boiling it, with the hope it will work again.
The SD is one of the most reliable
devices out there, so if this one is proving a problem, get an email sent to the Supplier.
Your post is a little confusing though Dave, as you state you are loving it, which gives the impression its working well, so, it makes me wonder if you are also using the SD with other attys, possibly the 901, without the adapter? If so, then the adapter for the 510 has to be faulty.
Its often the case with adapters, that some wont work with specific brands of 510 atomisers, but I have not heard of that particular problem with the SD. So, once again, I say report back to the Supplier.