Could be flow, placement, instability.... have you been doing water changes or just dosing and skimming? Temp?
Overall, this is a pretty new tank and it is going to need to have time to stabilize. You are diligent in trying to get everything within norms but don't move too fast. Changes in a reef tank are like turning a cruise ship. Too fast, it becomes a destroyer.
Seriously though..... move that nem away from the wavemaker. They also make little foam covers to cover the intakes. It is not uncommon for a new to get sucked in and that is very unfortunate for the nem and the rest of the tank.
Good luck with it!