Very fast follow-up from the Support staff! I thought I would post their suggestion for others to view. This may not be a fix for anyone else and I am not suggesting that anyone else try this for a similar problem. I have made the change to retention rules as suggested below:
Windows 10 is adding an extra partition to many users' systems as part of the upgrade process. It does this by reclaiming data from the end of C:. This resizing of C: breaks the backup chain.
You should modify your XML definition to include this new partition to ensure that you can recover your system successfully.
In the Macrium Reflect Default Settings there is an option under the Backup settings called Retention Rules. Where it says "Retention Rules Apply To" you can change the option to All backup sets in the target folder. This option determines how Reflect handles retention conflicts when you have backups from different sources going to the same target folder (which is effectively what has happened here with the resizing of the C: partition).
Hope that clears things up.
Looking at the scheduled backup routine I've been using, sure enough, this additional partition was not included.
Desktop: Windows 10 x64 / Macrium Reflect 7.1.2833
Laptop: Windows 8.1 x64 / Macrium Reflect 7.1.2801