Because I have set my parry to be exactly 20, when in armor, based on my DEX. My parry is now 19 when in armor, which means I have lost 1 AC from DEX and another point of AC due to the loss of parry. The whole point of the armor I have is to allow 16 Dex which I could reach by a single use of abyssal might or a dex buff. Now I'm 4 dex away from reaching that.
So I am not sure what caused it, but I am absolutely sure that my dex score has changed. And likewise, my con as I have stated above.