I have a Boiler staging control and a couple of mixing controls (classic series). It doesn’t seem as if the mixing controls are providing enough heat and the building is under heating.

Both the Boiler staging controls and the Mixing controls have a ‘Boiler Minimum’ setting to protect the boiler(s). The boiler and mixing controls are reading the boiler temperature at different locations, supply vs. return. Therefore, you must set the ‘Boiler Minimum’ setting on the mixing controls at least 20°F cooler than the ‘Boiler Minimum’ setting on the boiler staging control. Otherwise the mixing controls back off too soon while the boiler control thinks everything is okay.