I can't find anything directly on the ATO website to state that a SMSF has to insure Gold Bullion it has invested in.
Can you please confirm if insurance is required?
Trustees have a duty of care over fund assets - SISA S109 Investments to be maintained on arm's length basis.
This means that trustees would be negligent if they did not insure assets for loss, theft, etc.
Your SMSF auditor will confirm this.
https://www.relianceauditing.com.au/can-superannuation-funds-invest-in-gold/