This is something I noticed last night. When using Lissandra's E as Coven Lissandra, the claw itself will briefly appear upon cast but then disappear afterwards, forcing you to mentally time when to activate it again. This bug only affects the visibility of the claw itself as all other aspects of it still work as intended.
1) Pick Coven Lissandra.
2) Use E.
3) Watch carefully as the claw itself is visible at the start of the ability then invisible the rest of the time.
This bug is only on the Coven skin, as I used the Program skin in another game and the bug wasn't there. I was also using a Chroma and on the Twisted Treeline so I'll do some more testing and see if it's a chroma, a skin or a map exclusive bug.
UPDATE: I've been unable to reproduce this bug since posting this, so my guess it was either a one-time thing or it's extremely rare.