Had a similar problem earlier this year (RAB knows!)
My theory is that she just slowed down laying to the bare minimum for some unknown reason. Then, with a strong colony collecting nectar and pollen, she began to run out of space as it was filling up with food.
On advice of a more experience BKA member, I decapped some stores and scored the wax where there was pollen in one frame. Placed frame in centre of hive and they cleared it, repaired the wax and she started laying in it.
So it depends on what's going on in your hive re stores, space, state of frames, queen OK (no damage), spraying of crops locally etc. etc.
Look at what going on, make a note of it and the answer is there somewhere - thanks RAB !!!