I was not able to find any online product info from Clorox which tells me this is just a rebranded bag of salt from some random manufacturer. Anyone with a bag of this stuff should carefully read the product labelling to see if there is a country of origin on it or a different manufacturers name. Most of the Clorox Pool & Spa products are NOT manufactured by Clorox but by other companies and they just use the Clorox name on the packaging. In fact, I did a little careful digging and it turns out that Clorox simply has another shell company in place which acts as a partnership with a Canadian chemical manufacturer. So, in reality, when you're buying this stuff, you're paying for the name and that's about it.
The fact that staining is randomly occurring leads me to agree with JamesW that this salt likely has yellow Prussiate of Soda (aka, sodium ferrocyanide, Na4Fe(CN)6) in it to act as an anti-caking agent. When the potassium ferrocyanide is added to pool water, the ferrocyanide anion (Fe(CN)64-, pale yellow) can be oxidized to the ferricyanide anion (Fe(CN)63-, dark red) and leave a stain. Over time, the ferricyanide will slowly breakdown to leave ferric iron (Fe3+) behind to form iron oxide/hydroxide stains.