Well, the good news is that you switched to another cable and there is no issue, meaning your earpiece connectors are fine. Also, you mentioned about the helmet, motorcycle? Makes me wonder if due to sweat some moisture accumulates on contacts or maybe the wires are bent in some weird way and start to wear out prematurely. I assume you are talking about the cable with in-line remote. Could be either an issue at the mmcx connector or headphone jack connector. It almost sounds like a headphone jack connector, like something is bending and wire starting to break. One thing you could try, use contact cleaner,
DeOxit, in case if there is some issue with contacts of the connector. But I'm leaning more toward an issue with 3.5mm headphone jack; maybe just replace the cable under warranty?
In some case right angled 3.5mm connector is a godsend, but in other cases, depending on how you carry your dap/source - it introduces an extra wire bend which going to affect the cable, accelerating the wear and tear.