I can now consistently reproduce this bug!
My Amiri has both damage reduction feats, so any damage she takes is reduced by 1.
When multiple characters take damage, lets say from warden of runes, and this damage is reduced to 0 by her feat, the next character rolling the check will have the die roll offscreen and will get a 0 as result, but take no damage from the failed roll!!!
Also, when Amiri is the only character taking damage from the warden I cannot play weapons for the following combat check and trying to do so will instead remove the base strength / melee die. However, going back to main menu and resuming (or restarting the app) fixes this problem.
It all works fine if Amiri takes more than 1 damage though.
I hope this way to consistently reproduce the bug helps you guys!