Sometime it happens that the performance of an app decreases (or it starts to work not properly): this may happens with some resources consuming apps like the Facebook one. Every app has a reserved memory where it can store locally data and may be after some time the stored data became too big and/or may be those data are not handled in the better way.
A possible solution could be to uninstall that app and install it again … but there is another easier and quicker way in every Windows 10 device, so both on PC/tablet and on a smartphone 😉
You must go to Settings -> App & features, select the proper app, then click on its Advanced options link: in that page are shown all the details of that app and, among them, its storage usage. Clicking the Reset button all the local stored data of that app will be deleted and it is like it was just installed. Probably you will have to insert again your credential to access that app if this requires authentication, but then surely you may notice that its performances will return as they were at the beginning!! 😉
The following screenshots were taken from my Windows 10 mobile device: you can notice that before the usage storage is 428 MB and after the reset it is 161 MB, mainly the size of the app (only 16KB of local data against the initial 266 MB!!)