If price increases over a time period, what is the best explanation(s) if hash rate goes down?
The price was pretty stable and very low for most of those three months, it only picked up significantly in the last few weeks. 

As the price had been low and in a long-term down-trend, the profit margin would be extraordinarily slim, making the market even more competitive. This should have limited additional investments by current players, and curbed interest of new players to enter the mining market. It appears that any technological advancements have only driven out less efficient rigs and improved profit margins slightly. 

As the acquisition cost of mining rigs represents a significant portion of the total operation cost, I would assume that short swings would only cause less efficient hardware to be turned back on for the time being, but a major wave of new acquisitions would need a pronounced long-term up-trend. Even if the current swing is perceived as such, order, delivery, and taking into operation will lag behind the trend some weeks to months.