My kitchen slide was doing the exact same thing when new. Sometimes it would open, sometimes it would just make the ratcheting sound as if it was fully extended.
The service tech adjusted this slightly towards the frame and that corrected the problem. You may find this under your slide when extended. He said it was driving too far in and jamming the gears, or something like that.
![](https://i.imgur.com/tfwnw6fl.jpg)
Serious Warning: This bell stop assembly adjusts how much the slide closes. If yours has this you can try slightly adjusting it towards the frame a quarter turn at a time. Count your turns. Put a mark on it before you start turning. If you adjust it too far towards the frame the slide Will Leak. IIRC, he turned mine 3/4 turn to get it to work properly and still seal properly.
Hopefully someone here more knowledgeable will chime in on this.
I hope this helps