I believe that’s the case. The doublers use a fabbed welded steel adapter with the splines cut off of a slip shaft from a drive shaft. So the shafts are male/male and the coupler female/female, that coupler seems to work around a lot and eventually broaches out. Alignment seems to be difficult, and wiggle seems to be an issue. I think both combined are the Achilles heel of them.How are the shafts the collar is connecting being supported. Single bearing each? Single bearing and pocket bearing?
If they're not supported well on both ends then they're gonna move around. For a single male/female shaft pair with a long spline section this can result in tolerable misalignment but double the splines and double the slop and everything is going to wear more.