Can not edit a note sometimes

[Franciosi 0]

My Evernote [Version 6.8 (453748 Direct)] on Mac [10.9.5] is acting strange. Sometimes the ctrl+b stops to work. Sometimes I press Enter inside a note in the app and nothing happens. So I command+tab to any app, after return to Evernote and sometimes work. Sometimes I need to select another note and after the same note again to work. If the note is already opened in a new window, I need to close it, and after open it again. Sometimes I need to close and open the app again to make it work.

I have like 300 notes.

Why?