M,
I doubt anything is 'wrong', but it really depends on how your skimmers are plumbed.
I suspect that the skimmer that does not work if much farther away from the equipment pad, compared to the skimmer that does work.
Do your skimmer have individual control valves at the equipment pad, or are both skimmers on the same pipe at the pad?
Show us some pics of your plumbing before your main pool pump.
Thanks,
Jim R.