Trying to edit the Dark Gray Canvas for a custom basemap that does not have buildings...
I successfully saved the new tile layer, but upon inspection there is a sliver cut out of the [land] layer at zoom level 10:
Look just SW of the Pocomoke City label

Here is level 9:

And level 11:

The same gap in the basemap shows up on other styles, such as World Street Map (night) and Light Gray Canvas.
I believe there is an issue with the cache for [land] at level 10.
Thanks!
This sliver of missing land has been resolved since your posting. While the Esri Community is a great space for sharing info, issues, and enhancement requests on our products... for our basemaps, this Basemap Feedback Service page should be used. It allows directly marking up on the map. Draw a perimeter of the area and add brief text about the issue. We look forward to the use of this service by our users.
https://www.arcgis.com/home/item.html?id=fd83089ab5634391bf96cb7076b73c09