How to Resolve Issues with QGIS 3 Processing Dialog Layouts on MacOS

If you are using QGIS 3 master builds on MacOS and encounter issues with the display of processing dialog layouts like this:

The problem is caused by the custom designer widgets python module for QGIS. To fix it you should rename or remove this file

mv /usr/local/lib/python3.6/site-packages/PyQt5/uic/widget-plugins/qgis_customwidgets.py \

/usr/local/lib/python3.6/site-packages/PyQt5/uic/widget-plugins/qgis_customwidgets.py_

The actual location of this file may vary depending on your system. After removing the file, restart QGIS and you should see the dialog layout restored again: