Clutter or obstructions that block the sensor are the first problems to look for if your door won t close or in extreme cases open at all.
Garage door will not close unless i hold the button.
They can easily become mis aligned due to bumping twisting and loose mounting.
If anything interrupts this beam of light the garage door will not close and the ceiling light on the opener mechanism will flash as mentioned in the previous step.
It is a craftsman.
The first was checking and removing the light in the opener certain lights or looseness of fittings can cause frequencies that can disrupt the remote signal and is in play when the door is freshly opened but not when it has been closed for a while which explains the asymmetry.
Depending on the brand.
One sends a beam of infra red light to the other.
My garage door will open by just pressing the button once but to close it i have to hold in the button until it fully closes.