Manual Liftgate Latch

I have a manual liftgate on my 2010 Edge. When I close the liftgate, the latch
will not engage completely and then liftgate doesn't latch closed.  This
causes the "Liftgate ajar" message to pop up on the dash and the lights to
stay on for an extended period.
I took it to my mechanic, who swears it is latched, but it isn't. I have had the
problem for a while now, and they said I will now have to contact Ford and
possibly get the whole door replaced??? That sounds crazy to me.

If I manually push in the latch on the latch assembly, while the door is up, the
message on the dash goes away. So, I know that it isn't an electrical/sensor
issue. Something in the latch assembly is not getting engaged when I close
the gate and it causes it to only latch part way.

Is anyone out there familiar with this type of problem? Any help or guidance
you can provide is appreciated, as it is a safety issue.  Air pressure, bumps,
etc, could possibly cause my liftgate to pop open.