DS is used everywhere in HikaShop. The constant is automatically defined if necessary when the HikaShop main helper library is loaded, so that's not a problem.
If the manual generation works and that the cron task work, then the only thing left is that the configuration of the plugin has been changed in a way that the plugin in not triggered by the cron task anymore.
For example, if the auto update option is turned off, if the FTP credentials are not correct, if the "Last Update" field value is in the future in the options of the plugin or if the frequency is really big (a few months/years for example)... Remember that these options unit is the second.