I have not heard of any relationship between Iodine and seizures.
That being said, what part of the world are you in? How old is the dog?
Many parasites can cause seizures due to toxins they release, various lungworms are notorious for this. Have you had any blood work done? Is there an elevated eosinophil count? Has the dog been coughing or seem to get winded more easily? Panting a lot? All signs of parasitic infection. I suppose if there is a parasite condition and the Iodine is causing die off the toxins from that could cause a seizure.
How about drinking water? Has the dog been drinking/urinating a lot? High blood Sugar levels also cause seizures.