@Butters it seems my announcement of success was premature as the problems have recurred today. I will describe chronologically what has happened.

6th Sep
20:00 – Firmware revision 5.40 successfully loaded

7th Sep
06:50 – Leave home
07:10 – Passed through morning location without problem
07:20 – Arrived at work and reconfigured Bluetooth (had been cleared by firmware update)
17:00 – Leave work
17:10 – Passed through evening location without problem
17:30 – Arrive at home and set Home location on Garmin using Current Location option

8th Sep
06:50 – Leave home
07:10 – Garmin crashed at usual morning location
07:20 – Arrived at work
17:00 – Leave work
17:10 – Passed through evening location without problem
17:11 – However, Garmin crashed at location 1 km further than usual

I am now thinking this is all Bluetooth related, but once configured, disabling Bluetooth does not eradicate the problem