I am currently testing the development version darktable 3.5.0+2525~gd1f02a42ef and have already noticed in the git versions of the last week that there is a problem in the collection module when using the folder view.
Until darktable 3.4.1 it was like this: if you clicked on the top folder in a folder structure, all images were automatically displayed in the lighttable recursively downwards from this folder in the folder structure.
Now, in the current git version, you have to explicitly expand each folder to see the contents.