It is probably not air, but water caught between the structure (pool walls) and your pool liner. Too much water in the ground could be the cause. Check the water level in the dry well and ensure it stays low. A water leak from the pool could also cause the water to get under your pool liner.
https://espaceclient.trevi.com/detaillants/papeterie/puits_assechement_corrige_2018_bilingue.pdf