We need more details. What geometries? Polygons, lines, points? What kind of extents? Where is the File GDB located? A network drive, local drive? What kind of network speed do you have if it's a network drive? Are you accessing the File GDB via the API at all or just in ArcMap/Catalog? Did you notice when the slowness started or was it just randomly 1 day?
Have you tried copy pasting all of the feature classes into a brand new File GDB? What version is the File GDB and what version are the clients? If you have multiple people editing, that should really be done in SDE, from what the Esri Documentation states.