Sona has in my side of view a Bug with her Passive and Thunderlords.

A small amount of champions currently can proc thunderlords with the Bonus damage thread of their assiv! Lux, Kha, Lulu, Bard are all examples of it because they got some BONUS damage as thread on their passives. Sona has with her Power Chord a passive like the other Champions that deals a extra amount of Damage on her Autoattack that get used after 3 abilities. But it dont apply a bonus Stack on Sona to proc Thunderlords. Her not changed Autoattack damage thread and the Power Chord passiv damage thread doesn't count as stack for Thunderlords but it should. Instruction to recreate the Bug: 1.Play Sona with Thunderlords 2.Press 2 abilities to stack your passiv 3.Press Q and 1 autoattack on an enemy Champion 4.Now you see that Thunderlords dont Proc 5.Attack the enemy Champion again in a short duration 6.Thunderlords will proc if you attack the enemy fast enough because The Q and the aa and the other aa count as Thunderlords Proc.

The combo of Sona with q and passive aa should apply 3 thunderlords stacks not just 2 like it does at the moment. Sorry for my text im not a natural english speaker.