Transmission Problem?

My ML320 is a few months old (3k miles) and I've noticed something with my transmission: at highway speeds, sometimes when the engine downshifts, the transmission pops into neutral. I've also noticed this when I manually downshift to D4 and then try to up-shift back to Overdrive? My local benz dealer is so backed up that I can't get a service appointment for two more weeks. IS IT DANGEROUS FOR ME TO CONTINUE DRIVING, and is this a common issue?