Key Frame Glitch?

OminousAutumn

I read other threads from 2014-2019 and was wondering if there is a fix yet?

i have finished my animation and it's great. Time to simulate, but now i can't add a key frame for the Y value of my model. I need them to start in the air at 0 and end in a laying position at 30. When I add a key frame and change the values, it automatically deletes itself when the timeline marker changes frames. Bug? Am I doing something wrong? 
 

it worked at the start with my initial 0-30 sim. Then I keyframed 30-159 and now I can't keyframe Y before 30.