NGP not always calculated

I have a question about the NGP (normalised graded pace), which is not calculated for all activities. I have included a hike for which it wasn’t calculated. Does the applied formula not work below a certain pace?

One of the reasons I would like to know this is because very hilly trail ‘runs’ (hiking up, running down) don’t get an NGP, which seems to impact the calculated load.

P.s. the load of hikes is generally absurdly high, but that is a separate issue