If your Hugi hub disassembles like mine does (a newer Hugi tandem hub), it is possible to take it apart and check the star ratchet with no tools at all; in fact, I carry a spare star ratchet so that I can do a field repair if necessary.
Remove the rear wheel and take out the skewer. Lay the wheel down with the cassette side facing up. Grip the cassette with your fingers between the spokes and the largest cog and lift straight up as if you were trying to lift the cassette off of the cassette body. A small amount of force may be necessary, and of course, you'll need to hold the wheel down as well. I find that curling my fingers up with the knuckles against the spokes usually does the job.
What makes this work is the fact that everything is more or less held together by a captured o-ring in the axle. When the wheel is mounted, the skewer makes sure that things stay together.
If you do manage to get it apart, pay particular attention to the four parts that you will liberate- a washer that goes under the star ratchet in the hub side, the two parts of the star ratchet, and the spring on the cassette body side. You want to get these back into their correct locations to avoid turning your tandem into a fixed-gear ride (with disastrous results for the chain and rear dérailleur I might add).
Once you've got it apart, it's really easy to see how it all works, and by extension, what's wrong. If nothing's actually broken, clean it all up and apply a *light* coat of grease- too much grease in there is probably worse than not enough as it can keep the ratchets from engaging. A little grease on the o-ring will help when you push it back together.
I'm not familiar with the compact type of hub you mention, but this procedure is probably worth a try. It certainly takes a lot less time to do than it does to explain.
Also, DT Swiss has manuals for all of these hubs on their website. It takes a little poking around to find them, but they are there.
Good Luck with the repair-