Intentional RF emitter failing unintentional emission test?
Well possible that an unit that has approved building blocks fails as one new system. The cumulated total emission can be too much due a simple summing or due increased individual emissions caused by new interactions. Do not rely only on "all my parts already have the certificate".  

Do not believe? What interactions????

Think about a radio device and a too high voltage power supply for it. The higher voltage can easily raise the spurious outputs too high or the output at the legitimate frequency can have too high power.