Whitco Tasman MK2 security door lock

I have recently replaced a worn out Whitco Tasman MK2 ( triple locking ) security door lock and now I am having trouble turning the handle when the door has closed, it seems to jam.

When the door closes in the door jam the secondary bolt hits the striker plate and then the main bolt throws fully into the mortise (?). When you try to turn the handle to open the door sometimes it feels jammed and you need to give it a sharp turn to open it. I can replicate the problem at the same intermittent frequency by holding the door open and pressing the secondary bolt so that the main bolt operates, so the problem is not anything to do with it jamming on the jam or anything.
While the main bolt has not fully extended the handle turns perfectly every time.

During testing when the problem happens if I lift the main bolt a fraction or push it back in a fraction the handle turns perfectly. I bought it from a locksmith and when the problem first occurred I took it back to the shop, where it worked perfectly, but they swapped it for another anyway and I still have the same problem.

Is there some trick with these that has escaped me?

Jon


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