How can I turn off grid squares in my online arcgis.com map?

[660030371Exeter]

How can I turn off these squares?
They appeared randomly and now won't disappear.

Thank you!

[PeteCrosier · Accepted solution]

I've seen this happen when not at 100% zoom in Chrome - here's a couple of related threads:

Whitelines in basemap arcgis online? 

https://community.esri.com/thread/101373