I do not know what causes this, but there seems to be some combination by any of the following:
- often switching between japanese and chinese
- using more then one browser at the same time with skritter
I am currently using ungoogled chrome for character writing due to skritter being bugged with firefox (i already opened issues for that), but i use firefox for everything else including studying reading, meaning, tone.
Also because i am learning chinese in parallel to revising japanese i quite often switch between the two. Today i have been doing this quite a lot and i had to disable study kana 3 times after suddenly being prompted kana again.