the pure silver and pure Iodine in Lugols may combine in serum to form silver iodide. i do not think this is as much of an issue with plain KI.
just remember, Iodine is out of serum in 24 hours but silver takes a week to make its way out of the body.
the health effects of silver Iodine are unknown to me and therefore the caution. thats all.
btw, silver is not a daily supplement. it is best to use it to get the desired result and then be done with it except an occasional dose, say every quarter to six months. its needed(my opinion, not proven) but not in very large amounts. we were much healthier when the two dimes we rubbed together in our pockets were 90% silver instead of pot metal.