Parts not visibile in main assembly, but visible in sub assembly

I've a main assembly say 'assy1.asm', it has a sub assembly 'assy2.asm', this sub-assy has a part say part1.prt. Now this part (is a hose made using piping) is not visibile in main assembly. But if you open assy2, the part is clearly visible. I'm facing this kind of problem for the first time.

I've checked all representations, unhidden all layers, unit systems, no regeneration issues and there is no extrude made in the main assy that cut throught this part.

I've tried to open the same assy in different creo in another system, the same problem exists. 

What's causing this issue & how I can fix this.