[glend (Glen)]

Ben, every ASI1600MM owner has problems with Alnitak reflections when shooting this area. There are some threads on CN about it. The reflection is caused by the mono sensor surface reflecting back into the sensor cover glass (note I am not talking about the camera AR window). Panasonic make these sensors for ZWO, and when they produce a mono sensor without the Bayer matrix, the surface is more reflective than a normal OSC surface. Panasonic use their normal sensor cover glass on these mono sensors, which are not anti-reflective. So that is something we have to live with, and short of trying to change the sensor cover glass (with say some Astronomik MC-clear AR glass, which in all likelihood would destroy the chip), there is nothing that can be done other than exposure management or framing to avoid Alnitak.
ZWO are aware of the issue, but Panasonic has been unwilling to produce these sensors using different cover glass, which us understandable given the small batch size ZWO buys and the impacts on production runs of changing glass used. Of course it may just be a matter of cost.

Some folks claim it is the filters used that contribute to the problem, but I see your using Astrodon filters so that can not be an issue in this case.