I found a staff +1 hydra. As expected i can now have 2 active in game.
I have now found a ring +1 hydra. With both staff and ring equipped i can only have 2 hydras active instead of 3.
Is this a known bug or intended but not explained?
The extra hydra is from the Serpentine Aspect
You can’t cumulate 2 identical aspects. That’s why one of the two is probably greyed out when you try to equip both.
You cant stack the same legendary effects. If you have multiple of the same effect you will only benefit from the strongest one.
You CAN have 3 Hydras though… enchantment, aspect, spell. 
Thank you. I was hoping against hope…