My phone started to have apps crash, some android apps would open then shutdown, and I was having all sorts of crashing and anomalous behavior from Mitakuuluu. I checked the System > About and saw my drive was 12.5GB out of a total 13.7GB
I guessed this lack of space was causing some of the problems.
I moved all my photos and videos and Mitakuuluu/whatsapp files from the main drive to my actual SD card. this saved me 1Gb-ish. I still couldn't find what was taking up so much space though.