I know sometimes if the sun is shining towardso the sensor it will start to go up before hitting the floor but this soundshould like you may have a misaligned sensor or one of them going out but this doesn't explain why it hits the floor first so my answer to you is that the travel distance setting on the motor is not set right it thinks it's hitting something besides the floor the settings for the door travel distance should be on the back of the box that contains the motor I'm sure this is what is causing your problems