Janome walking foot suddenly acting up - help?

[Wwena]

Starting yesterday, my walking foot has been falling off every time I raise it to the highest. It's so annoying!! I don't know what has changed. Typically I will sew a short bit (I'm doing binding on a hotpad), come to the corner, use the threadcutter (scissors button) and raise the foot to it's highest point, where it promptly comes loose and falls off. In order to attach it again, I have to lower it to the first raised position. It's like the upper feeders are pushing it off. Help! Has anyone else had this issue? I can't for the life of me figure out what has changed. I think I'm putting it on right, I can't figure out any other way it can go.

This is the part that comes loose:


This is when it's happening:


This is what it looks like when I've put it back on:


This is what the walking foot looks like from the back attached to my machine (the loose bit is not re-attached in these pics):


Any input is welcome!!