Early ovulation or false + OPK after Letrozole?

Tina
Hi ladies,
Wondering if anyone experienced any false positive OPKs or early ovulation due to Letrozole?
I took 5mg CD 3-7, Clear Blue Advanced OPK on CD 8 was definitely an open circle (negative), but yesterday on CD 9 it was definitely a solid smiley face (peak), suggesting possible ovulation shortly.
I don't usually ovulate (if at all) until at least CD 14 or later.
I would think that it's a true positive OPK since the day before the result was negative, but it skipped right over the flashy smiley. Would this be normal?
Any experiences?