The finishing topcoat layer is still sticky or tacky to the touch and doesn't seem to be curing at all despite adding the right amount of catalyst and mixing well.

This usually happens on very hot days Where the sun beats down on the top surface of the roof and heats up the deck underneath. This heat will inhibit the cure and will stop the topcoat fully curing.

If the correct amount of catalyst has been added then the topcoat will cure, it just might take longer than expected, check the roof after 48 hours and if it's still tacky then you can abrade the uncured areas and re-apply in cooler conditions.

In the height of summer always try to apply the topcoat in the later afternoon or if you need to leave it overnight then first thing in the morning.