Seems to specifically happen with Titan-Touched nodes, and primarily for herbalism but there might be other cases. The cast will go off, the spell will go on cooldown but no extra Rousing element will be generated, nor will there be a portal in Titan-Touched nodes case. Seems to be happening more and more often and it’s a significant chunk of gold essentially down the drain every time.
I can confirm this. Up until today there was no issues. Now twice it fails to do anything with the titan touched herbs. Wish I knew so I would overload something else and at least get something. 
This way please: Bugreporting - how to!