1. Check that the Master output volume in Mixcraft is set to 0dB. This will affect the volume of the mixed down file (if necessary, to avoid getting a distorted mixed down track, click on track 1 and holding down the shift key click on the last track, this will select all tracks, then scroll back up and ctrl+click any submix tracks to deselect them. Doing this means you can adjust all tracks volumes together using any of the selected tracks volume sliders, until you do something that deselects all the tracks again - Look at the final output meter at the bottom when adjusting all tracks volumes together so that you can make sure the loudest parts of your project do not go into the red).
2. If doing all this does not fix the issue, then you have a malfunctioning plugin somewhere.
Mixcraft 8 Pro Studio Build 418 (64bit)
AMD Ryzen Core 3.0 GHz,
2TB SSD etc, 40GB RAM,
Windows 10 Professional
Focusrite Scarlett 18i8 (1st Gen, USB2).