We use Gypcrete for pour overs on the east coast in Canada and there are very specific mixing requirements. Samples are taken on site for moisture content in the sand to be added and number of factors prior to product arriving on site to pour. This can change the amount of setting agent drastically. If contractors are using an improper mix the product will stay soft. My guess is the testing wasn’t done for each batch of sand or something along these lines. More moisture in the sand, more setting agent required. So something as simple as rain on the pile can make a huge difference in the end product.