stdragon :
You said you know what the source of the problem is, right? So what is it? Is it caused by a specific website you're visiting?
It's caused by a simple 3rd party app. I've downloaded a Music Player and its doing fine. And then one day i uninstalled the app due to some complications with the performance but i really liked that app, so a few days later i've downloaded the app again, this time, it gave me headaches. And like I said, i did a full reset for 3 times and then nothing happened. I've disabled the google chrome in favor of a private web browser which is a Firefox Focus and still nothing. Browser setting can't do any help. I've also searched for a suspicious 3rd party app and I found nothing. It's pretty useless and a waste of time. It popups during a the middle of my app usage for 3 times a day. Sometimes, when i start my phone then it'll popup any second before you do your thing.
It's getting pretty annoying everyday, I can't afford to buy a new phone because I only had it for 4 months.
My possible guess is the phones factory installed apps. Which most of it contains ads, so i had to disable them all to free up some space for storage because I never use them at all. I only wish phone makers have that function to completely remove pre-installed apps which were never used. Pardon for my speech construction.