The frame hinge not locking on one side can be caused by the trigger release not springing back into place. 

 STEP 1: 

To solve this, you need to reset the hinge spring on the side that is not locking correctly by; 

1. Removing the trigger completely (unscrew)
2. Using a screwdriver to pull the white internal shuttle back far enough so the spring resets (You will hear it)
3. Then check function by using a screwdriver to pull back shuttle, if working again it should auto-lock the hinge when the handle tube is lifted into place
4. Replace trigger and screws, and check function again

If the above does not work, then try the below. 

STEP 2: 

1. Remove the sunhood locator from the frame by undoing the below 2 x screws and pulling the sunhood locator away from the frame.

2. Check if the hinge will now lock. If it locks, replace the sunhood locator (2 x screws)