I’m not even sure it is a thing for L&L, but every time I either switch from or to full screen writing view the grammar checker gets enabled (you know, the thing that ships with macOS). I do like the spell checker but the grammar checker is, well, for the brain dead. The only solution I have found so far is switching it of manually, time and time again. This gets old very fast. If someone please could help?
Have you turned it off in System settings?