When you place a Wall Covering on a Wall with Openings set at the base of the wall (0mm / 0″) you may see some problems. If the Covering is not configured correctly, the Cladding will fail to extend below the Openings.
In the example above, the left opening has no cladding below, where the right opening is correct.
To make sure cladding extends correctly, you should set Openings > Edge Offsets > No Cladding will be placed below this height  as highlighted below:
For ArchiCAD 19
For ARCHICAD 20