HARDFAULT in mesh SDK ble_mesh_v0.9.1-Alpha access.c

I have the mesh serial example working with nRF51-DK (nRF51422). I am now trying to run the same code, via the nRF51-DK debug port, to a nRF51822 QFAC (32Mb) based board. It downloads and runs up to the following line where I get a HARDFAULT:

static void access_state_clear(void)
{
    memset(&m_model_pool[0], 0, sizeof(m_model_pool));

A break at this line shows the m_model_pool memory is allocated (it's static anyway) and accessible. Stepping over this line gives a HARDFAULT. What might be causing this?

The nRF51-DK (nRF51422) and the nRF51822 QFAC have the same memory maps so I am using the same build settings.

Simon