LH test not accurate ?

My husband and I have been TTC for 4 years. We have always used ovulation test kits. Last year when I went to a fertility clinic they actually recommended me use ovulation tests kits to easily track my ovulation so i could get a vag us or what not. Well I decided to leave the fertility clinic bc it was getting pretty expensive so I went my regular OB and told him about how letrozole is what we used at the clinic and how it worked to make me ovulate around cds 18-21, well fast forward to today I am on my third round of let with my OB and I got a + LH surge on June 7, well they had already scheduled me a day 21 progesterone check on June 9 so I went and got my blood draw knowing it was too early to tell. Today my obs nurse calls me to that based on my progesterone lab it reveals I didn’t ovulate, so I tell her about my lh surge and what not and she goes on a whole spill that LH tests aren’t recommended when taking clomid/letrozole. Has anyone heard this before? Cause I have never heard this. And this was my 10th medicated out of the 4 years and I have always used OPKs.