From High Back to Low Without a Peak

I've been using the Clearblue Fertility Monitor for about four years now. It detected a rise in Estrogen followed by a surge in LH after having my first child, which resulted in my second child. It did the same thing after my second child, which resulted in my third child. Now, I am using the monitor again to await my first ovulation after my third baby to hopefully have baby number four. However, the monitor has been doing something it has never done before. It has been givine me High readings that last five to seven days and then going back down to Low readings. It's my understanding that if it starts to read High, it will continue to read High until it either detects a surge in LH, or you have to reset it (this has happened to me before). But two separate times now it has read High and gone back down to Low on its own. Just wondering if it is programmed to do this or if it could be malfunctioning?