Does this happen to all of them? If so it makes me a bit nervous since it doesn't seem like the RME has a very good warranty. The manual seems to state that it is only 6 months. I did get mine through Sweetwater who provides a 2 year warranty but if the encoders really only last a year it seems like this DAC will not stand the test of time.
Who could know really.
As far as warranty, I really don't know why they put 6 months, seeing as how it's country related. I doubt they'd leave anyone high and dry for a manufacturing defect for example. And this issue was present on their forum where the guy in charge says to send it in for a simple encoder swap. The device otherwise is flawless.
As for standing the test of time, I have no doubt it will have any issues as I've not seen anyone with any other issue other than this (or just complaints about why they don't have and ADC in their DAC when the ADI 2-Pro is the one with the ADC, so that's just confused people and such).
It's hard to really know though how widespread this issue is. That could only be confirmed by the company.
It also fluctuates. Like when it's really humid, this issue is severely minimized. When it's dry, it gets worse for me personally.
The only thing that can go wrong on these sorts of devices seems to be thermal cycling degredation (this goes for any device that produces massive amount of concentrated heat without a heatsink to aleviate some of the instantaneous heat rise and fall). Which is basically every single DAC that I've seen on the market outside of the Sabaj D5 (though it seems they got scared of Amir's review about how it takes time to warm up the device for optimal performance and I've seen some shipping without heatsinks). RME claims their PCB design does a fair job, but I'm not sure why you would want the PCB doing the work of a heatsink in all honesty. Ideally DAC makers should be using the body of their DACs and having contact with dies that produce heat to distribute the load. This holds true for basically any electronic component producing heat in my opinion. But alas this seems to supposedly be a non-issue on DACs seeing as how no one uses heatsinks, you mostly see them inadequately used in power amps at best. (though I am of the opinion 99.99% of audio device makers skimps on proper thermal management for some reason).