G'day @ZOS_GinaBruno, this bug is still present in the latest patch. I can confirm that bows, dual-wield, and staff blocks do not stun... well, not anything. Easiest way to reproduce, for me, is Clanafear, when they jump. Normally a block will stun them, but now I get the "is immune" message, and they are fine.

@SlippyCheeze : on which platform and megaserver are you playing TESO? ZOS needs that information to investigate the issue which you reported. (Please read and follow the Guidelines For Bug Report Forum).

In my PvE experience, "Stunned" is a status effect which is possibly the result of a Block. A Light Attack, Heavy Attack, Block, and Bash are, respectively, "abilities" which are intrinsic to the character's use of a weapon (including Fists, while unarmed).

A successful Bash always stuns the target briefly, unless the target is "immune". Else, whether any status effect is applied to a hostile target when the other weapon abilities are used is pseudorandom. The probability of a status effect being applied to a specific opponent or class of opponents might be quite high -- so the status effect seems to be applied "every time" when a player charcacter uses a weapon ability (such as Block). In fact, however, the probability is never equal to 1.0 (certain).

You specifically mention blocking an attack by a Clannfear. In my experience, when a Clannfear jumps to attack my character from some distance away, and my character uses a Block in anticipation, the Clannfear is usually knocked-back and might also be Stunned. But that does not always happen. What the Block does prevent is that my character is not knocked to the ground, so I don't have to subsequently interrupt (Bash) the Clannfear's continuing attack before my character can get up and counterattack.

For other abilities, applying a Stun or other status effect such as Concussed is pseudorandom, unless the outcome of an ability explicitly includes applying a status effect to the target(s), as described in the ability tooltip. Again, some targets might be "immune" to the status effect, and the murky "Target is immune." message usually refers to that.

Note that a player's character can also be afflicted by a status effect as a result of an attack by an NPC, MoB, or a device such as a trap. Usually that is a pseudorandom event, too. However, it might occur "automatically" for specific attacks and/or for attacks by specific NPCs, MoBs, or devices (such as the Clannfear "jump" attack discussed above).

That said: it would not surprise me if the ZOS developers have inadvertantly introduced a flaw ("bug") which affects whether a status effect is applied as part of the outcome of using a weapon ability. Nonetheless, deliberate changes are ordinarily documented in the Patch Notes. So we need to review those before posting a bug report about any apparent change in combat or in any ability, particularly.