This looks to me like the mount got to a position where it could no longer carry the weight, and guiding couldn't make up for the difference. I've watched this happen in real time with my iEXOS-100, and rebalancing resolved the issue. My issue resulted in subs that looked identical to this.
A cable snag would do it too, but I'm thinking that is something you would have noticed.
Explore Scientific iEXOS-100
William Optics SpaceCat 51 APO
ZWO ASI1600MM Pro, ASI533MC Pro
Canon 5D, T3i (Both Astro Mods)
William Optics UniGuide
ZWO ASIAIR Pro