The item has gone missing today. Does anyone else have this issue?
Reference found in this Google search but just a listing not found error:
Solved! Go to Solution.
Interesting note that most of the Web AppBuilder applications that reference the "Missing" item will not load any other layer, just the WAB framework of banners, widgets, zoom in/out, etc.
Others open fine and just don't include the "Missing" item in the layer listing.
It is back and working as usual this morning.