It is extremely frustrating to see prices increase while you are contemplating making the booking, especially when the increase is so extreme.

There's no evidence that UA utilizes individualized pricing based on search history (and that would be much more than just an algorithm!). Rather, it's likely someone bought a ticket - the pricing algorithm can be extremely sensitive to small changes in inventory. It's entirely possible the price will drop back down. You might also consider checking to see if/how the SFO-DEN segment is impacting the pricing.