Yes, you can't re-equip the item, because it thinks you don't have enough stats.
But it's only visual, at least in my case. Sometimes I had to reload 2-3 times to make it work, other times it was perfectly fine until I reloaded.
Basically your items above 5 of the required stats will show as greyed out, but in fact they're still equipped. For example, if you have a warrior that gets this bug, you'll see as if you were attacking an opponent with your fists, but you're doing full damage of your weapon - with all your stats.
It also messes up your skillbar and Action Points bar too, so it'll appear you can still attack with 2 AP left, while wearing a 2-hander (and you'll hit them with your fists, but in reality on the host's screen you're not doing anything, unless you have at least 4 AP).
I assume it has something to do with the invited person, haven't seen it happen on host yet. Did you try trading save files and change host? Might solve it.
So my guess is, it has something to do with character being corrupted on the client side, while on host's side it's perfectly fine. Also whenever the host took over my "bugged" character, he saw everything is as it should be.
Hope these pieces of information or deductions can help you and/or the Larian guys.
