Okay, so you've definitely verified that the _task_hash that's generated for an incoming example is the same task hash that's already present in your dataset?
Setting 'exclude': [dataset] in your recipe shouldn't be necessary, since this is the default behaviour.
Also, another thing I noticed in your code: input_keys=("id") should be input_keys=("id",) or input_keys=["id"] – otherwise, the argument will be interpreted as a string instead of a list of keys.