Yup I blundered the grave explosion protection, but it's fixed now. To recover graves, you should be able to place a block where the grave once was.

I'm sorry I didn't catch this bug sooner.

If the plugin does not recognize the items and doesn't return them, you're going to have to check and give the items back manually as there is nothing I can do. However, check your configuration and that your inventory has enough space, as there is an option to keep the items that didn't fit inside the grave.