Running the bluetooth mesh example (samples/bluetooth/mesh/) on a nrf51822 results in a Hard Fault. The provisioner is meshctl (bluez). After successful provisioning I disconnect from the mesh, when connecting again the hard fault appears:
I'd bet the recv thread stack overflowed. It's already at 97% with only 32 unused bytes based on the above log. Try increasing its size to something bigger. The Kconfig variable is called CONFIG_BT_RX_STACK_SIZE.