I have 22 collections, all of which are assigned to the same layout.
However, even after confirming that each collection is properly assigned
(checking the collection properties tab), they do not show up in
"Associated Collections" when inspecting the layout in the Layout
Templates tab. It seems that they all lost their association with the
layout. Only when I do the following steps does it show up: edit
collection properties, change the layout applied to default, save,
change the layout back to...