This has probably been already reported. But sometimes the shield doesn't work and sometimes it does. I did a few dungeons yesterday. On one of the dungeons I was at the top of the shielded scoreboard as a cleric healer with the devine aegis. But every other dungeon, it says 0 shielded. So I believe most of the time, this enchantment does not work. But works once in a while.
My devine Aegis is at mythic and unbound. When it doesn't work, I noticed that if I unequip it and re-equip it a few times, it starts working.