How does Yubo previously known as Yello remember users after reinstall?

Question

Okay, I have asked Reddit 3x and Apple once and no one could answer this so I am coming to you guys. Please be the ones to answer this validly. Okay, details. Yubo remembers my phone after reinstall and I do not know how. I have tried the following:

• Changed my IP Address using a VPN
• Change my IDFA through reset identifier which I now know is pointless as since I had “limit ad tracking” on the output would have been an output value of numerous 0’s (though this some how got me unbanned from the “Instagram” app, idk how tho)
• Changed my IDFV by...well reinstalling the app (Yubo is there only app so don’t ask about other apps from the vendor)
• Change my iPhones name multiple times
• Prevented the app from being backed up on Icloud then reinstalling
• I also logged out of the Icloud prior to using the app for the first time after reinstall

And that’s about it. I am aware the app may recognize: my phone, ios version and hardware. However, none of that is exclusive to my phone. I have read people having the exact same model and phone so i doubt Yubo is remembering me through that. I have never met an app so smart before, but I know some of you have probably been screaming this entire time one thing I have missed so please tell me what i missed and a way to change it without resetting my phone.

My device: Iphone6s and IOS 11