Internal Gear Hub Nexus 7
It sounds a little like you are shifting while pedaling. That's the opposite of how internal hubs work and will tend to cause the shift to happen delayed or never, and if done habitually for long enough is bad for the hub.
If you've got the yellow mark dialed and you're shifting only while coasting, and it's happening as you get into the slacker cable tension gears, it is possible there's a kink in the cable somewhere hidden by the housing, and it's causing friction that is making the shifting erratic.