Hello all, I have an update for you! We have found the cause of this issue and are working on a way to revert the change.
Our engineers have been investigating, but in addition to Janthir Wilds keeping everyone very busy, the issue with infusion stacking impacts other systems and made investigation more complicated.
As we've mentioned in the past, we are always working to improve every aspect of our development processes. In this case, we made a change to help us better test particle effects, and that had an unintended effect on the way infusions behave in the live game. We are working on a fix that will revert the change to infusion stacking and allow us to keep the improved testing functionality. We won't be able to create, test, and ship that change before the August 20 game update, but we do want to get it to you as soon as we can.
I'll update you when we have a good idea of when that is--in the meantime, thank you all for your patience while we looked into this.