Barn Owl nest box concerns

Hi,

we have 2 barn owls nesting in the meadow next to our house. The nest box has never been used in the 6 years we have been here. We’ve noticed that the bottom section has fallen open and this seems to be where one owl is sitting on eggs. We are worried that they do not have enough protection and if the eggs hatch the owlets could easily fall out. shoukd we leave well alone or attempt to fix the lower section closed? Any advice appreciated.