Try this...
Use this tread as representation only.

Uncheck single part boxes..

Add punch marks for nosings.

Create a separate detail for your treads and treat the plate object as a placeholder outline. If you make your master tread and group it together it's easier to copy around. Make the treads main part model role as "not visible" and weld them to your stair. Your detail will show the plate shape as your tread, It will ignore these in your bill of materials. It will show your custom treads in the BOM. We don't get sub assemblies so we have to cheat our way around it. Create the tread assy and name it first and create the detail. When you add it to the stair using the welds and renumber, it'll break the treads assembly association.
If this was my problem, this is what I would probably attempt.
Good Luck!
...and fix the kiss export issues.