I can’t really help you here, as I’ve had this happen an innumerable amount of times with Windows 10.
I fully believe that something in the Windows updates are purposefully screwing up dual boots, because every time I do any sort of windows update (even if it’s not an “upgrade” but just a plain update) it completely breaks the boot sequence when I have a dual boot set up. And most recently, I had to completely reinstall windows too because SOMEHOW it broke its own boot loader in the process and I couldn’t even recover that.
I hope you can figure out an easy fix to this, but in my experience, completely reinstalling Antergos (or any linux distro) has always seemed to be the easiest fix for me, albeit the most annoying one.
Hopefully you get a better response than what I have to offer though.