Not for me to find a definitive solution as I’m just a user like you. But when it gets unusable I just restart EndNote and it works better again for a short period. Rinse and repeat.
To EndNote tech support: it’s seems to be quiet here and no real official feedback. You might want to take control of this as to my mind, this is kinda embarrassing. And the longer this persists (like I said, it’s been an issue for a long time now), the more users will defect. I’d do it myself if it were practical. C’mon!