Speed (tempo)

Hi

I have the impression that my watch is not "following" me quickly enough in adapting the speed I am running. If I go quicker/slower it doesn't show that immediately.  This morning it took like more than a minute before it showed the change on the screen.

Every second recording is on, GPS+Galileo is on. 

Any help is welcome as I am training for a marathon & this is driving me crazy as I cannot seem to find the problem or solution.

Thank you

Nathalie