Not sure if this has been discussed before, but I often find myself unable to block at all. At first I thought it was a controller issue (but I wasn't going to find that out while in the middle of a zerg in cyrodiil), it's something that has happened several times in any area, usually logging out and back in again solves the issue, which isn't ideal when running dungeons as a tank. Sometimes it just solves itself.
I know that this isn't an issue with my gamepad since I can still bash and roll-dodge.
I forgot to do samples of those things on this video
https://youtu.be/vJVmqqIASA0
But if you see the video, you can see that when I hold the block trigger, the wayshrine interaction input turns dark gray - the game IS registering the input on my controller.
I'm not sure if this is a specific issue on the platform I'm playing or if it also happens on pc/ps.
From the time I was running a dungeon, I tried bashing, still worked, but if I recall correctly, it didn't consume any stamina at all (nor did the blocking shield appear in front of my character, when all my teammates DID display the blocking shield when bashing).
I don't know how to reproduce this issue, but if someone does find out how, it might be exploited for the upcoming bash meta builds where they can get away with bashing without consuming any stamina at all.