Hi Nick,
Would you be able to send us logs and the exported project?
You can capture logs using the Capture Logs application in /Library/Application Support/Blackmagic Design/DaVInci Resolve/. Running the app will create a log file on your Desktop. You may email them to davincihelp at blackmagic-design.com. Please capture logs as soon as the problem happens, and before restarting Resolve.
Other information that would be useful to know:
Does the render fail at a specific clip or is the failure random?
Does the problem happen only in batch mode rendering?
What format are you rendering to?
What format is your source footage in?
Vivek Vedagiri
Blackmagic Design