I just bought and installed the Lock & Load X plugin.
I'm testing on a short clip (less than 20 seconds) and the results are much worse than the original shaking of the footage. The rendered clip present a lot more movement and random variations in the zoom. Nothing smooth at all. After trying several parameter combinations I'm giving up and asking for advice.
I should mention that the original clip was shot at 1080, and I'm editing it on a timeline set at 720. Other than that the clip's speed is the same. Would this frame size difference be an issue?
resizing the clip should not be a problem.
In some cases FCP does not correctly recognize the clip's field order. In that case stabilization results can get bad.
Also, as Yuri mentioned, sequence in/out points can be a problem. Please clear in/out points until the clip is rendered.
Does the problem also occur with Lock & Load Frames ?
Just wanted to let you know you're not alone – I've been unable to get any decent results with L&L X. It seems to make motion and jitter much worse, exactly as you describe. Frames seems to work okay though. It's still buggy, but much less so.