Block not visible

The "Demonstration site reset" block is set to display in "Sidebar second" in the active theme. All other blocks assigned to "Sidebar second" display correctly.

The "Demonstration site reset" block is not displaying.

The block has no restrictions (not restricted to paths, roles, or content types).

I tried moving the block to the other sidebar. I tried changing the restrictions on the block (as I originally set it to display only for the "admin" role). I tried changing the permissions for the module (permissions for the module are currently set to be available only to the "admin" role; I unchecked all roles; I checked all roles). i cleared caches.

None of those actions resulted in the block displaying.

Any suggestions?