(not enough mana) but Auras and Heralds still work?

One of my Auras is greyed out and says "(not enough mana)" when I hover over the icon. However, as far as I can tell it is working. I'm pretty sure I have plenty of mana for them all to work with some to spare.

I have 3 Auras\heralds active and I can see the mana reduce as each one is activated. They are all showing as active in the top left corner. It seems like this is some sort of bug or I'm missing something (the latter is very likely).

https://freeimage.host/i/KsyH9yv

https://freeimage.host/i/KsynxQs

https://freeimage.host/i/KsyoIN1