The part that shows as 9/16 in. thick is modeled off axis. If you select it and zoom in your can see that the geometry is skewed in the bounding box.You’ve drawn the part slightly off axis.
FWIW, I also note you have Display Precision set rather coarse for a project of this nature and you have Length Snapping enabled.
I would recommend setting the Display Precision as high as it goes for the units and turning off Length Snapping as having it on can lead to errors.
FWIW, I copied the top rail component from the middle over to replace the white one. Notice that the end panel and the rail do not align properly. This is the cause of the off-axis geometry in the white component.
I made all the changes you suggested. The end panel was misaligned. I moved it back 1/16 and the panel was skewed and refused to show as 1/2 thick is now happy!
I did have an odd thing happen. I had to resize the cutout for the kick board when I moved the panel and as you saw it was to high which created a gap.
I hid the kick boards to make it easier to resize the cutout and now they won’t unhide?
I tried Edit, Unhide, All to no avail. I can see them in the component list. If I select View, Hidden Geometry and View, Hidden Objects I can see the wire frame?
Sorry for the newbie problems.
thanks again for catching my mistakenly placed panel.