Occasionally a random button without window appears

I'm on Windows 7 Home Premium.
Until now I thought it was a title of a Windows 2000 window (contrary to the windows theme I use) :


It is not a process and windows doesn't give it focus, so no input like Alt+F4 can interact with it. It is always in the foreground but does not appears in the taskbar.

I cannot tell if it is linked to a windows service somehow because I have dozens of them, half without description in the task manager and I don't know what they all do.

I ran Antivir and Malwarebytes multiple times and neither detected anything, I cleaned my registry, and even restored my system and it changes nothing.

Usually when it appears I can temporarily get rid of it with a normal reboot.
It appears only occasionally usually one or more weeks between each time, completely arbitrarily.

Does anyone know what with this and how I can get rid of it?

I clicked on it so often that it crashed, it's Avira's own ipmgui.exe / in product messaging and it somehow fails to load properly, probably cause of adblockers or so.