This only happens after I equip new weapons/shields (on any character) and if I don't hover them after.

The big question here, and you'll understand it after watching the video is, if I don't hover the item after equipping it, which damage values is the game taking when attacking?

youtu.be/IN_evPuY2vI

the bow is +4 to hit because it uses Dex and Shadowheart has 14 (+2) + she is proficient with that type of weapon (+2)

the shield give +2 armour making her curent total 17... if you equip her with the gith armour Lae'zel starts with that would push it up and later on there is a magic shield that gives her a total of 20 base armour

there are also spell buffs that can temp add armour but the key point of Larian Ui is you get the shield bonus even if you are currently using your range weapon

as a side note consider swapping out the mace for a dagger with high Dex that would give her a much better to hit chance for the loss of a small amount of base damage

the Mace is +3 1 for 12 str and 2 for proficienty if you use a Dagger its Dex so thats currently +4