Cannot use captured soul

Pressing X just does nothing.
Workaround: talking to Sin applies the captured soul and removes the item from inv.
This happened when I had the boss in a mirage, and I ended up with two copies of the captured soul, might be related.

Also, I discarded the second copy before talking to Sin but some people in Global reported that having both in the inv when talking to Sin causes the buff to be not applied.

PS5 Pro

As to the last part:

Using a captured soul the first time in a league unlocks that pantheon for all of your characters in that league (once they reach maps). Using a 2nd copy of the same captured soul disables that pantheon upgrade for the specific character that did it. This causes the pantheon text to be red.

The reasoning behind this system is that you may want a particular mod for some characters but not all. For example, you may want the 50% reduced effect of chill mod on most of your characters, but it is actively bad on a Reverse Chill build.

They should probably fix the two vessels at the same time thing with Sin, and probably also make it so you only get 1 vessel when completing a boss in both the mirage and the main map.

I captured 2 souls today and in both cases, I used them only once and these turned red right away. This happened on my first character in this league...