If your water is really hard that grist was unlikely to be able to buffer enough alkalinity to make for ideal mash conditions. that could very well have something to do with your problem. Get a couple gallons of RO water, this should cost you less than 1 dollar most places if you bring your own container, and try again with that water and some calcium chloride and gypsum. With RO your grist will have no problem buffering all the alkalinity in the water. you might even have to add some but bru'n water will guide you through that process.
if you want to eliminate or indicate mash chemistry as the heart of the issue, don't change anything else about your process. don't double crush or thin your mash ratio or anything, just switch out the water.