There is something probably I'haven't very well understood in the blocks Administration->Coonfiguration->Blocks
The "show hide" column shows the open eye icon: trying to hide the block, the icon does not change to closed eye nor the block disappear from the courses. When clicking on the open eye icon belonging to the "Social activities" block, all the open eyes icons change to closed eyes and all blocks hides from the courses layout. Clicking in the closed eye icon belonging to Social Activities does not allows the other blocks to reappear, it is needed to click on all the closed eye icon in the list before clicking in the icon belonging to Social activities.
Where I'm wrong?