This box was able to control a maximum of 2x 24" monitors via both display ports.

If I have 27" and larger, one is connected via Displayport, the other via an external (!) HDMI connection via the laptop. Various things play a role here.

There are also other phenomena.

2 external screens can generally be connected via the display port. It also depends on the resolutions and refresh rates of the screens what the Mac can do (1080 HD goes up to 60Hz, higher resolutions with 30Hz...).
Sometimes an update of the driver of the docking station is useful/helpful.

I work with my laptop and another monitor, which works perfectly.

As a supplement, the MacBook is equipped with four Thunderbolt 3 ports.