These are reflections, could be internal...
Great Engineer's Thinking, Dear Arjay
In my Idea, and It happend to me long time ago. just 1 small reflective dust on the front of UV. filter, that create the UFOs on the dark sky for me. I hope that are the real UFOs, that I can sell to the Newspaper for millions Us Dollars.----Ha, Ha, Ha.
Dust on the filter would not cause "UFOs". More likely dust on the sensor. A filter will increase the chance of ghosts, a dirty filter will increase the chance of veiling (a lack of contrast).
If gear matters: 6D, M3, Samyang 14/2.8, Voigtlander 20/3.5, EF 24-105/4, EF 35/2.0IS, EF 50/2.5 macro, EF 85/1.8, EF 200/2.8II, EF 400/5.6, EF-M 18-55/3.5-5.6, EF-M 55-200/4.5-6.3, Ext 1.4x, Lifesize conv, Ext tube EF25, 430EXII, 270EX, Yongnuo 603C