I realise Achievements is not the most robust of Bb's tools - but I've recently found an issue related to custom Badge Images after performing a course copy in Learn 9.1 Q4 2017 CU6.
After copying Achievements into an existing course (regardless of whether the Adaptive Release rules have also been copied across) the custom Badge Images do not appear to also be copied, as they do not appear when viewing the Course Tools > Achievements > Edit > Select Reward settings page.
However, once the Achievements are redeployed (and if necessary the Adaptive Release rules reconfigured) the custom Badge Images do indeed appear to students when viewing the "My Achievements" Tool section.
Is anyone out there able to confirm that this is also occurring in their environment? I'd like to submit a known issue to BtB purely for the purposes of documentation, but would first like to get confirmation that the issue is not isolated to our environment.