I'm not sure if anyone has experienced this or not, but I have been playing for a while and started noticing that when I block sometimes, I drops during boss fights at times.
For example, if I am fight a boss and know they are about to land a heavy attack that I cannot avoid unless I block/roll dodge at the last minute and I am blocking, it will drop my block immediately before the attack lands. This is very frustrating and it is not a stamina issue. It causes a lot of frustrating deaths in dungeons and I was wondering if more people have run into this.