Downgraded to 5.3.5 and now the problem is gone. Sorry if you wanted some investigations.
Yes i remember that i tryed to hide it with CM, didnt work, but maybe thats the cause.
Edit: Problem again. it happens when i run
ssh email@example.com lipc-set-prop -- com.lab126.scanner doFullScan 1
When i had less Books on the K it didnt happen,
In CM its not displayed when not visible on homescreen.
could really be that FS is not sane, know how to fix this? remove books completly and upload em again? I'll take a try