Has anyone experienced letrozole/femara being effective one cycle and not another?

I felt I had strong positive ovulation results my first cycle ( didn’t result in pregnancy) and this second cycle I and fairly confident that I didn’t ovulate. Unless something wonky happened with testing and I just missed the window, I just don’t know that it’s happened this month. Blood test is this coming week to confirm or verify if it did or did not happen.

I’m so confused

Has anyone experienced this?!?