How to find out which app is trying to open spam websites?

I've recently bought a new Android smartphone. After setting it up and loading my contacts onto it I thought that would be it. Now after some days, every time I unlock the phone it takes a few seconds before it opens the default browser and opens some spam website. I tried to see what was causing it. I removed any apps I didn't know I could trust, but the problem persisted. After trying to solve it for some time I gave up and reset the phone to factory default. Now after having it reset to the default it ran without issues for roughly a week before the problem reappeared. I tried to uninstall some apps in order to see if they were to cause of it, but nothing changed after doing so. However I did notice that if I turn off the wifi it won't even try to open the browser (I haven't tried mobile data since I don't have a bundle). This makes me feel like it might be related to something on the network but that wouldn't explain why only that phone would have the issue when there are at least 6 android phones on that very same network. I hope that there is someone who can help me find the cause of this issue and help me solve it. TL;DR When unlocking my phone, it opens the browser and tries to open a spam website. But only does so while connected to the wifi. Things I've tried so far: - Factory reset (only helped for a limited time) - Clearing the browser cache and all related data - Removing any app I don't know to be reliable - Attempting to find what triggers it (seems like some type of internet connection is required??) The device is the Doogee Shoot 1. As for the browser, the default is set to be the Android browser, but if I change the default it would use Chrome just as well. It seems to really just use the browser that is set to default.