While grinding I have been experiencing inventory overflows, but the game has erroneously been messaging that I have "x too many soul stacks", and pointing me to redeem stacks of souls before continuing.

However, regardless of however many stacks I redeem, the error persists. I had tried redeeming stacks and then resetting, but the error persisted.

I found I could clear the error by navigating to the character screen and selling excess runes.