MapQuest has discontinued their open tile sources.
For this reason, you may see bad tiles or error messages if you are using "Open Street Map from MapQuest" or a map source that uses it as an overview map.
If you press the layers button at the top, then find the "More Map Sources" button and look under Worldwide, you will find alternate sources.
These include Thunderforest:Outdoor and Thunderforest: Landscape
In the latest version, we will redirect Open Street Maps to the Open Street Map Neighborhood view from Thunderforest.