This same problem happened sometime back also, but this weekend, while drawing initial water from the newly topped off water tank, through hot water and cold water, we had a very strong sulphur smell that eventually abated after use for a day or so. We don't drink tank water, but shower, dishwater etc.
I drain tank at end of season, add antifreeze to lines, in spring I remove antifreeze, add water with minor chlorine, about 10 gallons with maybe a cup of chlorine, drive around and then run through lines, and again drain tank before filling to use for the season. At this time, I open the valve for the hot water tank, so that gets fresh water to.
We used the unit for a long weekend mid summer, and all I did for this weekend was add to the water tank. First use of the water was horrible with acrid sulphur smell. If we let water run, it would go away. After setting unused for several hours the smell would return. It finally went away by about the 2nd set of showers on the second day of use.
What am I doing wrong here?
(Been an RV user since 93!)