I've been looking around here as I was running into the same kind of issue, then I'm posting my little bit of experience about it in case it could help someone in any way.
Basically I managed once (at first use) to get my D3300 capturing correctly without any extra shutter control device, but then when wanted to use it for real it was not working anymore (shutter not released / "failed to expose" issue).
I've then decided to go for a fresh install before to go for purchasing a kind of device mentioned here, and guess what...it's running properly at the moment (able to get any kind of capture, short and long exposure, FITS and native formats, etc.)
No special costomization, just an install from scratch on both client and server, moving the reflex power mode from "medium" to "long", and putting it in Manual mode before wire.
Nothing really factual I assume...but a least it proves that it can work, and as also reported earlier, sounds like a damn bug somewhere.