You can have more than one LH surge throughout the month; this is why opk's are beset with problems. These assume that women only have one such rise every month and that such a rise is immediately followed by ovulation. Both of these assumptions are not true.
Interesting, I had an unusually peak on my fertillity monitor but no EWCM. Was a week early but last period a week late. Do you think even a fertility monitor can detect a surge unrelated to ovulation?