There is case in GPS module init code where gps_ubx_reset_sensor_type(); gets called, and in turn it does
and writes to status-> lastStepTimestampRaw with status being uninitialised yet. This invalid access causes BusFault on F3.
Unsure what happens on F4, but it might lock up the flash from further writes instead of generating BusFault.
I am fixing this for a moment by checking for status ptr validity before setting the value, but somebody more familiar with gps and ubx code should verify it.