I am also experiencing lag in version v10.1.7. For example when double-clicking on a note in the note list, it takes 2 to 4 seconds for the note contents to appear in the new window.
I installed the new version 10 on my iPad and iPhone and tested if I could reproduce this issue. And it looks like it’s solved! I can now switch between other apps and Evernote and Evernote retains the note and place in the note when I come back to Evernote. Very happy with this 🙂