After Some Test I Found This Out :
The source of all bugs is **Fiora** - Having her in your team can cause other bugs to trigger such as the following :
Note that all these bugs can be triggered **ONLY AFTER 12 MINS** into the game, not before it
Master Yi can become invisible upon using his Q.
Pyke can also become invisible if he uses the ghostwalker boots and enter a terrain while he's in his W.
Fiora herself can use her W without cooldown.
I'll update this post if I find more bugs.
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