Marianna got same issue with healing skill. She put one pulsing ring above ally that never heal
That's not true, the skill does heal over time. Like every "over time" ability there are no numbers visible. The fact that her heal is relatively small might give the illusion of it not working correctly. Especially when the tank has a lot of HP. Let's say for example on Elric 1 inch of his healthbar represents 10k HP while on Tanya the same amount equals 5k HP only. Now Marianna cast her skill and let's say for referrence it heals for 1k HP the bar of Tanya will move more visible than the one of Elric.
Hope this is coherent for you