after months of working this issue, i am 99% sure the problem is with hunger thirst or fatigue changing statuses while in vats. The solution to this is to download 2 mods. The first is called survival options, and will allow you to disable hunger thirst and sleep. The second mod is called surviving the wasteland, and adds these 3 things back in in its own way. After doing this, I have had zero freezes in vats. Please try this, im pretty sure it will work. Credit to pectrius for finding this initially. If this works for you, please spread it around reddit and such.