LAP pace and Graph pace not the same

I'm using Zwift Run pod (Settings set :Always on Speed and Distance) and on my last run ( I noticed that PACE shown in graph is completely different from that in LAPS. I noticed that also during the run, kept an eye on pace and saw a pretty huge difference when the LAP summary alert popped up.
So what could be happening here? I did reset the pod recently, so it's probably not accurate (will fix that), but why there is difference between graph and LAP pace? Graph pace acquired from POD, LAP pace from GPS or something like that?