Game Mechanics: Question Armor Class Rating Fluctuations

[ezri]

Hi,
On my Bard/60 Inyahin my in game armor class keeps fluctuating between 10xx and 11xx (all stats are unbuffed) between days. I'll log on one day it'll be 1035; then log in the next day it'll be 1135 and then a day after back to 1035; without changing any gear.

On the 10xx days even if I switch to my highest AC gear, I can only get up to 1075; on the 11xx days I can nearly get up to 1200.

This is the gear that I wear most of the time.
Magelo_Blue:Inyahin_Elbereth
AC wise I can swap in Imbued Granite Spauldors and Sarnak Battle Shield.