I used the file that Ed supplied, so I never made the Pattern. I made a new file from scratch and created the Pattern.
I created a circle, a slot profile and a couple rectangles, etc.
I activated the "Array Pattern" tool.
Filled in 12 Cols and 6 Rows. Enter.
"Leave source copy" and "Fit" were the only options active.
I selected the Circle.
I "V" snapped to the bottom-left corner of the inner rectangle.
Then snapped to the bottom-right (X) and the upper-left corners (Y).
Then used "Finish" in the Local Menu.
The pattern is made.
I repeated for the 'slot'.
I activated the Simple Extrude tool with Compound Profile active.
I extruded the outer rectangle.
I could've held the Shift key and selected the 2 Patterns, but opted to just make a box.
I activated the Imprint tool.
I selected the face on the extrusion, then set the parameters for the Chamfer on the top & bottom.
I also loaded minus 3 in the height field and locked it.
I selected a profile and let it extrude. Due to the large amount of circles in the pattern, it took some time. That's why I lock the Height.
Enter, then repeat for the slot pattern.
I tried to Imprint both Patterns at the same time, but the programs crashed. Too much math??
I originally used the Fillet options in the Imprint tool, but that slowed things down too much.
Hopefully something is useful here.
Designer, Deluxe, (Professional, Expert, Basic), Platinum
Windows 10 Pro (1903), 64-bit