Showerthought: last Tuesday my 8 hens gave me 9 eggs and I felt like a chicken genius for about an hour
Then Wednesday through Sunday they gave me 2 total and one of them was soft shelled, so I'm back to Googling oyster shell amounts at 11pm. Did a hawk flyover spook them or do yours just do this when the weather turns?
Check for a hidden nest first, because a hawk flyover usually won't stop them from laying for five days straight. Ours do this exact thing when the days get shorter or a storm rolls in, and it can take a week or two for them to get back on track. For the soft shell, just make sure they've got free choice oyster shell and skip the midnight panic, since your mileage may vary on how fast that fixes it.