[Maks]

I had a similar problem a couple years ago. It turned out to be the slide controller. Each slide has it's own and should be installed close to that slide.
In our unit (3790rd), they are in the storage compartments under each slide. As any electronic device, one day it works and the next day it doesn't.
In my case, one side of the slide would open but the other didn't. It wasn't the motor or the ground. I eventually sourced the problem to the slide controller. But to get by temporarily, I figured out that if you switched the plugs from motor 1 to motor 2 and vica vera, it would work. But you will have to reverse the function. In other words, to open the slide, you'd have to press CLOSE. Then to close the slide, switch the plugs back and press CLOSE again.
That worked for me but no guarantee it will work for you.
Also, if that doesn't work, you could take a controller from another slide and switch it out with the faulty one.
All temporary methods until a new controller can be installed. The removal / replace procedure is very simple so you should be able to do it yourself. only issue is getting a new one...... expensive.