When you render in Mocha Pro Standalone, renders are temporary cached image files in your Results Folder. If you close Mocha and un-check “retain cached renders” on exit, Mocha will delete all the temp files.
In the plugin, cached renders are not retained between open sessions of the Mocha UI in order to make sure you have the most up-to-date source from the host. And any temporary renders are stored in a temp folder you can specify or leave Mocha to set to default.
We recommend that you export your rendered results to another output folder with File>Export Rendered Clip for proper backup.