It's very frustrating and it applies to new as well as one's with a little age on them. Some people do not use them anymore and some are going back to the manual models.
The motors across the board on these fine products are weak. Any extra load like water or moisture can stop and start them.
Also a low battery could be a cause . When you are experiencing this problem, are you plugged in ? (truck or 110v )
Make sure their is no tension on the arms to restrict things causing the already weak motor more stress.
On one of the Dometic models, you have to remove an end cap and unscrew a hex screw and use a center webstrap, having a second person to hold that strap certainly will help.
It gets hand rolled with use of a center strap to control it. Once its closed, the screw and cap get replaced and you DO NOT USE it until you have it serviced by a tech.
You can download pdf's from dometic as well other mfg of these awnings.