I don't know if this helps anyone. But I wanted to relay my story which is still undetermined.
In late 2016 I was diagnosed with temporal arteritis, about two months after having sinus surgery. All the symptoms were there including a sore scalp, extreme pain in my jaws, the back of my scalp, my eyes, and temples. I also showed evidence of some ischemia in my left eye. While my biopsy did not show evidence of GCA, my neurologist, ophthalmologist and ENT all agreed that it was temporal arteritis.
Still my rheumatologist had reservations. She thought it may be a sinus issue. I was treated with prednisone at 60mg per day for two months. The headaches resided within a day of starting the infusions. And we had to go back and forth with doses as I began to wean. It took a year to get off the prednisone and I have remained free from symptoms since.
I'm relaying this in the realization that the symptoms of temporal arteritis may also be indicative of sinus issues. I don't know that I will ever find out the cause of my symptoms, but the same treatment as that for temporal arteritis worked for me.