Question Stop root animations over-extending?

Hey, I've been having problems with one of my gates. Every time I open or shut it, the animation slightly over-extends on the way down so that when the gate comes back down it goes through the terrain. Play it too much, and you can't even go through because it doesn't rise or fall enough. I'm stumped here. I don't know how to stop this, or why it's happening. I've made and remade the animation four our five times with the same effect. It has happened in my other game too. I'm thinking of just using physics and a move script - but that may not always be possible. Here are all the details I can think to include:

Root animation playing the same animation three times (for gameplay reasons), but even when you do it with one animation it's just more subtle. On the way down the animation is reversed with speed -1. I've tried multiple other settings, but nothing really totally fixes it. animation generated by recording. Doesn't matter if the model is a basic cube or my own custom mesh.

Any ideas what this is?