Help, with my confusion please

Cathryn • TTC baby #1 🇮🇪 🇺🇸

Glow says I started my Lh surge cycle day 15 at 5pm but why is cycle day 16 so dark ? Is that really my surge ? This is a non medicated cycle. It wouldn’t matter so much but we’re using frozen sperm so I know the life span is way shorter than fresh.