Mortality rate in layers from onset of lay till peak of lay

Hello. I run a farm with 13000 Hyline Brown layers. They are 22 weeks old and I have 3- 5-6-10 birds dead per day. The mortality increased at onset of lay. I have this problem only from onset of lay till peak of lay. Then the mortality returns to 0.1% per week. At necropsy there are no sings of any disease. The egg percent is growing fast and there are no broken eggs or shell eggs. The vaccine schedule is OK. The nutrition and management are OK.(in my opinion). So, what is the normal mortality in layers from onset at lay till peak? Thank you very much for your answers.