Iv noticed it in pve as well, kinda frustrating when the npcs go to heal and you try and bash to stop it and nothing happens, also heavy attacks are not always hitting
I had it happen in sewers on a trove scamp a couple of days ago, was his first attempt to portal away and 6 bashes didn't stop him leaving. Also had it happen in maelstrom arena on the giant Argonian boss where bash only sometimes interrupts his scream (coz I accidentally killed his mates)
As long as this discussion does not relate to today's update, have not been in-game today, bash is interrupting npc characters just fine for me. There is a small window for targeting.
With that, some played skills cannot be interrupted unless they have changed that though the player can be knocked into the air which essentially stops the cast.