Page load time in Looker is way off

We have asked this question before but never got a clear answer.

We feature a simple bar graph in a Looker Studio dashboard with page generation time as a metric. Metrics has been set to average (AVG). The values that are returned result in page generation times of 30 mins or more.

Yet when we put the same data in a custom report, that same data return page load times of several seconds which is what we would expect so see.

See screenshots attached.

What causes the difference in Looker Studio and what do we need to do to get this right?