Animate won’t let me add keyframes between keyframes. Please help!

Hello! When I try to add a keyframe between another keyframe, it won't add a keyframe. All it does is go to the next keyframe as if I simply selected the next one. It wasn't doing this problem before. My Adobe animate software and MacBook Pro laptop are both up to date. I even uninstalled Adobe animate and reinstalled it and I'm facing the same issue. This is very upsetting. What do I do? Thank you!