As someone who has owned this product for almost a year or so, I get this issue as well, but I found a partial fix. I tried applying the firmware that SMSL was providing through the website but it didn't fix the issue.Anyone else experiences headphone out just stopping for no apparent reason? The source continues to play, so USB isn't disconnected. Only way to fix is to stop playback, turn off C200 and back on
Turns out it is related to the Electrostatic Discharge problem that was discussed in this thread earlier. My chair would release static electricity every time I would stand up from it and then I would get the issue you described (no sound through HP out even though the device is still turned on and not disconnected, only restart fixes it).
Partial fix for me was that I put a cotton pillow (the pillow cover should be out of cotton and not synthetic materials to be more precise) to make the chair comfier but it also reduces the build-up of static electricity. Why I say it's partial it's because now it happens maybe once a day or once in a few days, however it's still better than any time I stand up from the chair. The issue has something to do with grounding, probably the chair isn't grounded properly because the wheels are plastic, but I even tried placing C200 on wood and further away and I would still get the issue.
Otherwise since this is my first post, thanks to amirm for all the work and measurements he's done so far (still waiting for DT 1990 measurements with both pads and EQ profiles). The C200 is a wonderful product were it not for the DL200 which is slightly newer and basically replaces it, the C200 would still be the king of this price bracket and class of products for me at least (despite this issue). I use filter 6 and honestly even though I can't hear difference between them, I trust the measurements and many facts pointing that Fast Linear is usually the way to go. The AMP in both C200 and DL200 should be a bit better to really round out the product, but the amp is really competent, it can drive many different headphones (K361, DT 770 80 Ohm, DT 1990 all on low gain 65-70 volume (K361 at even lower volume), also runs Sennheiser 660S great), as well as IEMs (Truthear Zero Reds, Simgot EM6L). I even tried running the DT 880 600Ohms, and while it can do so at high gain you had to go really high up on volume. Whoever needs a better amp can add one on top if needed such as the Atom Amp 2, Topping L50/L30II.