If you own a Janome Horizon, you should know that some of the automatic plate converters are defective. Mine broke a few weeks ago. The little tab snapped right off. I thought I'd made an error, but it was poor craftmanship.
The solution is simple - just replace the entire plate with a new one. I left my machine in the shop a few days so they could clean it too. The repair and cleaning were at no cost. Still, given that the 1/4" foot was also defective and replaced, I can't help but wonder what's next?
At any rate, be aware.