In Administer > Yamm > Common options you will find the Debug mode option. By enabling this option, Entity parser will provide a lot of output.
You can find this output in two different places:
If you enable the DataSync backtrace module, which is currently in active development, you should also be able to catch a lot of DataSync events and associated PHP errors or exceptions through DataSync admin settings pages.
In Administer > Yamm > Common options you will find the Clean state button. The submit function behind will run the hook_yamm_api_clean(), which per default will wipe out all DataSync jobs that any enabled Yamm submodule could have queued.