The Depower Line is for any of the Infinity Bars from Flysurfer and is the thick grey line that runs up from the chicken loop to the depower cleat and back down through the bar to the loop again. They seem to wear out especially if doing a lot of loops as it forces it though the plate in the chicken loop. They are pretty easy to change though it not broken.
Keep one handy incase of breakage when you aren't expecting it!
below is a video from flysurfer showing how to replace the depower line: