[john70t]

There is probably a load-limit-switch which reverses the motor whenever the door hits an object on the way down.
(It is very sensitive for a good reason)

So first thing to do is to disengage the drive;...

Check the door operation by hand without the motor involved.
-It should be silky-smooth from start to finish.
The door should naturally rest in the middle or near the bottom if the springs are at the correct tension left and right.
The roller pins should not slide sideways if the spring tensions are balanced, and the structure is square.

Use a scraper and flashlight and clean out the old crusty grease from everywhere.
WD40 also helps dissolve that.

Every single moving link should be lubed 110%:
That means door hinges, door rollers and slider pins, track, chain, and motor gear. Everything.

Use WD40 as a temporary measure.
I prefer synthetic sprays and light smears of synth grease for the long run on heavy load parts .
Too much grease turns into solid dust chunks eventually.

There should be nothing blocking ful smooth operation at the end.