I have been thinking about this since I use the fork lock on one of my bikes....
When YOU use the fork lock, with the forks turned, do YOU just turn the key hard to get it to lock? Or do you firmly but gently turn the key and move the bars a little to center the lock pin to the hole? I don't know for sure it's a pin and a hole, but you get the idea.
I ask because some bikes may want the forks on the fork stop for the pin to engage, but two of my bikes want to be just off the fork stop. If it's against the stop, there is almost not way to get the lock to work.
Just a thought,