Was in MP with Gary and my warrior had 3 different shield block cards. He was attacked by the enemy warrior with a bash, this proceeded to be buffed by a trait and and another bash, the animation slowed down and lagged a bit. None of my block cards even activated and i took over 10 damage. The warrior did it again on its next turn with one less bonus, and my blocks activated, two failed and the 3rd reflected it back. This was not the first time that battle i noticed the blocks not activating. It was always when the attacking player was npc and always when there were 3 or more buffs to the attack. Usually 2 bash bonuses and a martial bash skill trait bonus. Also notice this seems to slow the game down even after the action.
The slowdown is weird (and possibly worrisome, given your other thread), but the rest might be explainable. So, he hit you once without you getting to Block, and then he hit you a second time and you DID get to Block? You can't Block when your back is turned: it sounds like your Warrior had his back turned for the first hit, and then he turned to face the attacker (an automatic action) before the second one.
Nope he did not have my back turned. Neither my warrior or the npc warrior moved or changed facing during both turns so either I should never be able to block or should have blocked both times. Also i am doing the level 6 special zombie and skeleton adventure just now and I saw the block FAIL again. I am facing the skeleton, he hit me, the first thing to pop up was my armor, not my BLOCK ANY shield. Shield never activated. Next turn still no change in facing the same skeleton hits me again and this time the shield actives but the roll fails. I have been noticing buggy shielding since i started playing. I would not have noticed it so much if it didnt happen when I was very much depending on the shields. No slow down this time but there were no buffs involved and it was not MP
Next time, try to get screenshots ? Or use the F1 console to grab the log with the command 'clip' like how other testers have done.
Make note of what blocks you have on hand if that happens again, there are a lot of variations that have different triggers (certain amount of damage, missile et c). Can have some relevance possibly.