Rapid response vs FRER

How oddly weird is it that rapid first response test are darker for me instead of the normal first response the rapid picked up a line before the other fr did even now days later the rapid is way darker I thought I was having a chemical because the first response line progression been so slow in my opinion until I took a rapid and boom ! Test came back way darker has this happened to anyone before I knew something was up when the digital first response said yes but the line test wasn’t as dark