Essential Oils
I like to take an essential oil, go ahead a pick a favorite, douse a square of toilet paper, and suck it into the machine before you start vacuuming. It will cover the smell very well. I like lavender especially. Its not my favorite, but Tea Tree oils seems to reduce odor pretty well too. I'll mix it with eucalyptus since that is a more favorable smell to me.
As far as why the odor is more prevalent now, I have no idea. Maybe Sebo has made their bags more anti-microbial and are killing odor causing bacterial more effectively? Does Miele Make a Charcoal bag to add into the mix?