Yep same here, This issue also followed me from iPhone 6s to the iPhone 8. The only conclusion I can come up with is that it might have something to do with my iTunes account because the problem comes back even when I configured my iPhone as a new iPhone.
I use my Gmail account go log into my iCloud and such. Maybe it has something to do with that? Anyone else?
I am also trying your wallpaper theory. I also never changed my wallpaper from default to custom. Now I have!
And I really hope Apple releases a software update soon because this is just really getting on my nerve. We pay so much money for an iPhone because we all love it's functionality but this is just taking waaaay to long.