I am not sure what's causing it, but in certain cases (many nested folders? files?) loading the folder/file list in the dataset page can be slow. Here is an example:

http://imlczo.ncsa.illinois.edu/clowder/datasets/5ab972724f0c5cb235dad0ed?space=5953ba884f0c5558e1684bf4#page=0

The calls that seems to take the most are:

POST http://imlczo.ncsa.illinois.edu/clowder/datasets/5ab972724f0c5cb235dad0ed/updatedFilesAndFolders?limit=20&pageIndex=0&space=5953ba884f0c5558e1684bf4

GET http://imlczo.ncsa.illinois.edu/clowder/api/datasets/5ab972724f0c5cb235dad0ed/listAllFiles?max=20

GET http://imlczo.ncsa.illinois.edu/clowder/assets/javascripts/d3js/d3.v3.min.js?_=1532360534744

The last one makes me think that this might be related to the mime type visualization in the visualization tab, but I thought that was fixed a while back.