Luteinizing hormone is released in pulses roughly every 60–90 minutes, so two tests a few hours apart can genuinely look different even on a completely normal cycle. A test strip is a snapshot of the hormone in your urine at that moment, not a running average.
The other common explanations are practical: diluted urine after drinking a lot of water lightens the line, concentrated first-morning urine can darken it, and testing at inconsistent times of day makes the pattern look erratic. Most guidance suggests testing in the early afternoon, after holding urine about two hours, and testing at the same time each day.
Some people also have more than one LH rise in a cycle. The body can attempt to recruit a follicle, not complete the surge, and try again days later — this is seen more often with irregular cycles or PCOS, where baseline LH may sit higher and produce persistently near-positive lines.
What matters for timing intercourse is the surge itself: a clear jump from your baseline to a test line as dark as or darker than the control line. Ovulation usually follows 12–36 hours later. A wobbling low-level line before that is background noise, not a missed window.