I learned the first word for the Slow Time shout in the Labyrinthian dungeon, ages later I stumble upon Hags End and clear it. At the end of Hags end is a wall teaching you another word for the slow time shout except it didn't unlock anything for me i.e. no new word in the shout to spend a dragon soul on.

I check online and see that Korvanjund is the last place for this shout. I join the legion, get the quest to go there, clear the area and walk up to the word wall, i hear the chanting and usual sound effects only there is no swirly lights and no word appears highlighted on the wall. Nothing happens at all. The chanting continues, the sound effects are all there but the wall is blank and my Slow Time shout is still stuck on the first tier.

I reloaded a save game prior to entering Hags end, went directly to Korvanjund via legion questline and clear it, this time the wall worked and gave me "Eternity" word but didn't unlock the 2nd tier. I went back to Hags end continuing this save game and got to the word wall there, it fired off ok, swirly lights and sounds but also gave me the word "eternity" for slow time again and again nothing got unlocked, still stuck on first tier for slow time.

my eyes !!

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