Triple Triad Card drop rate so low that it is basically a bug

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Date & Time: 30/4/2018-2/5/2018
Frequency: Constantly happening
World name: Zalera
Character name: Caimie Tsukino
NPC name: Munglig
Party or solo: Solo
Area and coordinates: azim steppe x12,y33
Steps:
1. The NPC won't drop any card at all despite me playing him day after day for many hours, and with over 90% win rate. If you call this my bad luck with RNG, then the drop rate is simply unreasonably low, which I would gladly call it a "bug". Seriously, I understand card drops are intended to be a grind, but winning almost every match for 3-4 hours without a single card drop is extremely demotivating and very frustrating. It's not even a 4 star card or 5 star card, but just a 3 star. Whoever designed this is just wrong. This is a wrong design, and so it is a bug. Please fix accordingly. And please let us know about this in the next patch note. Until then, I give up collecting cards. Thank you.
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*Add more steps if necessary

https://i.imgur.com/gUxzIpU.jpg