Giant Hole Under Sourdough Crust

Hihi! Just started baking sourdough recently and I was trying the oval/batard shape but got this huge hole at right under the crust. The rest of the crumb is what I was going for - not too dense and not too open, so I'm curious what could be the cause of the huge hole. Is it likely a giant air bubble from shaping my dough?

Ratio:

• 70% hydration
• 20% whole wheat flour; 80% high gluten flour
• 20% levain
• 2% salt

My process:

• ~4 hours for levain to at least double in height
• ~2 hour autolyse
• Added levain and mixed (rest 30 min)
• Added salt and mixed (rest 30 min)
• Fold (rest 30 min)
• Lamination (rest 30 min)
• 3 Coil Folds (30 min intervals)
• Bulk ferment (3 hours | total time since levain added: 6 hours)
• Pre-shape (fold right side; fold left side, fold top; fold bottom)
• Shape (tried to degas a bit; fold right side; fold left side; jelly roll; pinch side seams together and dragged it around a bit to create tension on the seam)
• Overnight fridge proof (12 hours)
• Scored
• Baked in dutch oven at 500 degrees F (25 min) and then lid off at 475 degrees (15 min)