What is this at the bottom of my home screen?

Xperia XA2 Ultra, Oreo
This only appears on the home screen. It looks like a partial uppercase S. It disappears after I reboot but appears again after awhile. Any ideas on what it could be and how to get rid of it?

from Android Forums at AndroidCentral.com - Ask a Question http://bit.ly/2G6n3pf
via IFTTT