I have lumia 920 and win 8.1 cyan. I have some problem with my memory when I use storage sense it tell me my system file is 10 GB and other file is zero when I use storage check it tell me my system fill is 2 GB and other is 10 GB. other than different problem this 10 GB is a lot of space is there way too clean this amount of space
IT may be that both the storage check and storage sense categories file differently and has different parameter for "System files" (may be).
Also, try cleaning your phone by connecting it to PC. Clear browser cache and if that didn't help, take a backup and hard reset your Windows Phone to clear out all the data. and restore the back up.