Spring controller jitters during XY movement when FPS is uncapped

In the video you’ll see that during movement on XY axis, there’s jittering. This also happens when my FPS is uncapped for some reason, even though a friend told me that within the source code, the calculation is frame-rate independent.
In the video I posted I cap the FPS to 60 in the second half, and the problem doesn’t happen.
Does anyone know a solution to this problem?