VST3's loaded in my host DAW show only a portion of the UI, rendering the plug-in unusable.

Some DAW hosts on Windows have incomplete HiDPI awareness implementations, such as Reaper 6: https://forum.cockos.com/showthread.php?p=2211751.

1. Solution 1: Use the VST2.4 version of the plug-in instead, which will render correctly. This will preserve the HiDPI look of the DAW itself.
2. Solution 2: If the VST3 version is needed, disable HiDPI awareness in the DAW if possible. In the case of Reaper 6, go to:
   Options → Preferences... → General → Advanced UI/system tweaks... and change HiDPI mode... to Unaware.
   Close and Re-open Reaper, and the VST3 window will load correctly.