I have the same problem. For the latest EN 6.15.4, the EvernoteSubprocess.exe continuously uses 10-20% of the CPU. Interestingly, this does not happen directly after startup of EN, but only after I click on one of the notes in the app. After downgrading to EN 6.14.5, the problem disappears, i.e., the CPU load is ~0-1% when the program is idling.