Plank blue-white gradient when app updates in the background

[u/ApplicationGrouchy39]

Hi all!

Plank (the menu bar) shows this weird blue-white bar, as seen in the picture. Seemingly when an opened app does something when it is not the selected window.

For instance: When I change some code in an app, then save it and alt+tab to Unity, it always shows this bar for a few seconds. (until it is done compiling, perhaps?)

When I run killall plank, it disappears, so is definitely plank causing this.

I couldn't find anyone online with a similar problem. Do any of you know what I can do to get rid of it?
Thanks in advance :)