thomson_adam, id say its the timing,?
i use orwg, and i always leave for 15 mins,
try using one coat,
you may find that noting the time you finish applying adhesive and the wait time
and timing it, dont guess it,
*also vitally important prep! make sure both surfaces , hair system+ scalp are dry as a bone and squeeky clean,
*clean youre finger tipps with soap water or similar, you dont want natural oils from youre fingers hands mixing with tha applied adhesive,
*there is the possibility that youre unique body chemistry,amound of perspiration oil release ect will affect the bond ,its a case of trying diffrent adhesives,
but providing you cover the basics as outlined*
you should get a rock solid bond
anty