At the time I thought it was a good idea, I plug my FEL into one of the 2 sets of remotes on my MF563.
Sometimes the lever that choses which set of remotes is being used will not quit go to neutral but also not fully engaged.
When this happens I get similar results. I put a short bungee cord to the lever just to keep engaged.
If that's how you've got yours plugged in anyways. If not, ignore.