OneNote Synchronysationg problems

I am using OneNote for university. I have often problems with synch of my Notebooks in OneNote and i don´t know how to fix them. I also contaced support via chat and remote control and the also werent able to do anthing. 

The newest problem was that OneNote lagged my hole computer Ram usage was up to 99%. If I closed it, no problems. 

So I tried fixing it with clearing the cache. Because of that I lost some of my notebooks. Anybody that has an Idea what to do, cause I'm pretty upset right now, to put it kindly.

I also got that message sometimes:

I think it doens´t take the sceenshot so here the error code: 0xE000006B b6d09

unfortunately in german but the error code (Fehlercode) should be the same.

The otherone was: 

Error code: 0xe0000002

unfortunaly I don´t have the full one. There was an additon to it.