This is similar to the bug report at http://dev.cmsmadesimple.org/bug/view/10174 which strangely got closed without explanation.<!-- Html blob '[name of global content block]' does not exist -->
I looked at the admin log and besides ClearCacheTask, CGSmartImage_ClearCacheTask, and PruneAdminlogTask (all succeeded) there is nothing strange in it that would indicate something has failed. However, manually clearing the system cache fixed this issue.
What’s that, why is it happening, and how can I prevent that in future?