Derlin as much I understand is one of latest polymers in use for Aerospace parts, electronic & communication devices.
Lets admit that after all its a plastic and not a metal. Fine plastic threads can deflect easily compared to metal threads.
UNC 6-32 is a small fine pitch size of aproximately 0.8mm thread pitch.
The possible causes are that a ? mark shaped helicoil insertion tool is in use.
OR a plain mandrel type prewinder insertion tool is in use , these type of tools don't guide the helicoil wire properly & could make them jump over in case of relatively flexible thread flanks in derlin.
Best to use a Threaded mandrel TYPE-II prewinder of HeliCoil Part # 7551-06 to prevent thread jump over.
Further a marginally better shaped thus stronger thread in derlin can be created by using serial taps ; rough first & then finish.
Somewhat significant thread flank strength improvement can be observed by using thread forming / Roll taps . ( check derlin physical property on permanent deformation)
You can download HeliCoil technical catalog from website www.helicoil.in for further information & support.