How are legends on the print template generated?

Question

Good Day

I've noticed that for some of my map, the legend on the Print Template is missing, and I don't know why.  ex:

Compared to others:

All maps use the same "UniqueRenderer", which has ~200 settings in it, and on the two maps shown, they both forgo using valueExpressions', unlike all the other maps.  So what causes the legend to show up?   For the two maps shown, they're set up virtually the same way, the only difference would be the field they reference, but both use a string field.

Thanks

MikeVolz · Answer

There might be too many unique values to show up in the legend so the legend shows none of the values.  As a test remove most of the unique values and see if the legend then displays.