In Arms Maester:
High Evasion and Mass Evasion that provide 10% block chance. Either they are not updating the character sheet or they are not actually providing any block chance.

In Siegebreaker:
Salvatory Anchor and Elevated Gain. When both the same type of head and chest armor are equipped you lose the bonus of the piece that was equipped first. As in equip a Heavy Chest then a Heavy Helm you will lose the chest bonus, the reverse is also true.