Suspicious download message everytime I activate wifi

[datco]

Since two weeks, everytime I turn on wifi a push notification appears saying "Messages: download in progress" (rough translation, I'm using a German device):

Screenshot

Edit: Image upload doesn't seem to work. Here's a link to it: https://ibb.co/589xn8H

The notification stays on as long as I have wifi (no matter if home or free public one) activated and causes my device to heat up like crazy, there's also a blue dot on the text messages icon during all that time. It doesn't seem to actually download anything. If I click on that notification, it just shows me the screen to write a new text message. If I swipe the notification and choose options, all I can basically do is turn off notifications for the messages app in general, which I don't want. As soon as I turn off wifi, the icon and notification disappear.

I have the latest updates for my Xperia X Compact (Android 8.0.0). I looked up that message in Google and it might be the Stagefright exploit. I looked at the options for text messages and noticed that I had MMS download activated. I immediately turned it off, but despite restarting my device, this strange notification still pops up.

I also checked my devices for viruses with the preinstalled AVG app and Play Protect, everything seems fine. This notification even shows up in safe mode, so it's not a third-party app causing it.

I'm really clueless what causes this notification, if it's an undetected virus or a bug. The worst solution would be a complete backup of all my files and do a factory reset. Can anyone help me?

[Strampke]

The best solution is to do a software repair with Xperia companion.

It cleans up all the mess that has accumulated during a long time.

It will take you some time but you will be rewarded with a clean and speedy machine.

Do NOT restore all the old apps, just the most urgently needed.

Enjoy!