Screens Keep Popping Up About Phone cooling, Drink more water, Various ads, etc. Interrupting Things I am Trying To Do?

[Slapshot]

This just suddenly started a couple days ago. These things can pop up at any time, and can disrupt me being able to do things on the phone since they take up most, or all of the screen. I am unaware of any apps I have added, and cannot identify anything specifically likely to be at fault in my list of apps. This is driving me crazy. It's not possible, at this time, to do a factory reset on the phone. What is causing this, and how do I stop it? 

Thanks for any assistance.

[RetiredLeah]

The solution on an android phone is

(1) when the annoying ad/message pops up, immediately press the refresh button twice (the lll button at the bottom of the screen) then

(2) immediately restart the phone.

[John Fieschi]

I found how this trojan works and how to fix it.

Go to  Chrome browser > Settings > Notifications > In-App notifications settings > Allowed .

Click in the Url and block the website one by one on the list.

Done , no more Pop-up Ads on your Android phone.

 

[Ailurophile]

I had this for at least a month and finally figured it out!  Go to Settings, Apps, then sort your Apps by Last Used (wait a minute for them to sort).  "Plant Lens" came up as a recently used app, which I definitely wasn't using. So I uninstalled the App, and no more pop ups! The App with the popups, malware, whatever it is, doesn't show up in Settings, Notifications. For me, it was Plant Lens. I can't say that it will be the same App for everyone, because I don't know enough about the issue, but this worked for me! So relieved!