I believe @TrapsAndDews
are on the right trail. Googling "humic acid sphagnum moss" is turning up several hits regarding humic acid affecting sphagnum moss and even more advanced plants.
Besides what was quoted above to do about the humic acid buildup, I've seen it stated to use less peat moss...I guess this means go with more pure sphagnum moss...???
Also, plants can acquire the buildup just like the moss can and might be confused as "rotting" or "burning". One user uses a turkey baster to rinse the crowns of his sundews with distilled water, followed by a gentle wiping using a wet q-tip and then another rinse.
I think I'm going to use the paper towel and then give my sarrs a good flushing!