Same thing happened to me a year or two ago. I replaced the latch mechanism in the trunk lid and it seemed to help for a bit, but after a while started having the exact same problem again. It looked like it turned out the little bar in the trunk that it latches against had either moved, or been bent forward and the latch wouldn't catch it just right. I got a hammer out and banged the bar towards the rear several times and it's been working ever since. Been at least a year now. I don't know if opening it and closing it at least twice a day for seven years bent the trunk floor or moved the hook (kept my work laptop back there) or not, but it seemed to do the trick.