Sounds to me like something is being added/packed into the exe, probably recursively.
So things like icons, images, aka resources the exe could use so I would look there, at your MS Build file and see if you can spot it there, at least thats where I would start.
Alternatively a multitude of programs like this could also highlight quickly if you have resources packed multiple times inside the exe (or DLL). It might even be other DLL’s packed into the exe that could explain the size.
Anyway thats where I would start.
Edit.
And as if by magic, there happens to be this thread immediately underneath your post which might also help.
Msbuild example for Clarion - ide / Tips - ClarionHub