The latch for that is visible with the tonneau cover raised.
Examine it for any obvious problems, lube it up good with lithium grease and inspect the 2 hydraulic lines for signs of leakage.

You can latch the rear bow manually by using a 6 mm hex wrench on the latch when the trunk is open.
Press the rear bow down while turning the hex wrench, I don't remember which way, but pizzaguy ( Mark ) has a video on here you can search form he states which way latches.