Check the plastic retaining ring inside that holds the lower burr in place. Mine broke, but they're cheap and easy to replace.
https://www.baratza.com/en-us/product/ring-burr-holder-sp0101174?sku=SP0101174
Or if you have an ESP: https://www.baratza.com/product/ring-burr-holder-for-encore-esp-sp0102053