if filemetadate-extension is installed it adds an extremely slow MM-Relation to file_mata_data-table.
Please install this extension and try to open an fe_group record in BE listmodule. As more file-meta_data exists as slower the records will open. In our case we have 54.000 filemetadata records, and for each record it executes 54.000 queries to retrieve the title of sys_file. We have to wait nearly 5 minuten to edit an fe_group record. And please have a look into sys_file_fegroups_mm. It's EMPTY! So why search for things which aren't there?