Thanks for the advice, however I have now found out what was wrong. The griplock upgrade has a bearing ring and a compression ring that fit into a top cap with a green o ring in between.
The position of the compression ring and bearing ring in the top cap can vary a bit i.e, there is some play in where the compression and bearing ring can sit in the top cap. If these rings are pushed right into the top cap the green o ring is pushed inwards radially and can’t fit over the steerer tube. So to fit it I had to make sure the griplock assembly was still together as one piece but the compression and bearing ring had to be moved away from the green o ring to allow it to go over the steerer tube. I did follow the instructions when I first tried to install it, but it didn’t mention that the position of the parts in the top cap was critical. All it said was that it had to be fitted assembled together. When I fitted the griplock earlier today I followed the instructions and torqued the top cap to 1.7Nm and then set the stem. After a short test ride it seems to be working well but time will tell after I do some longer rides.