Help vague alert won't go away

[optimist2]

Anyone recognize this alert icon? There's no associated notification (that I can see), it doesn't go away when I clear my notifications, it goes away (temporarily) if I clear my cache, and yet it comes back after a reboot. I can't figure out how to get rid of it.

 

[SavageRobot]

With it being a different colour (I'm pretty sure since about Lollipop all notifications are white unless customised) I would guess it is an actual app running and putting that symbol there. Have a look in your running apps, is there something in there that could be suspicious? Things like system cleaners and battery optimisers tend to be worse than useless and would probably put something like that up there.

 

[androidmachine]

If it were white and if it were an exclamation point in the middle of that triangle, it would look exactly like the alert that I have on my phone because I have background data restricted. I agree that the yellow color makes it look like it was put there by an app.