Dependency TimeOut Error when making requests to Neptune

we have recently encountered a timeout error halfway through the loading process when making requests to Neptune for bulk loading from S3 (via AWS lambda), with the following errors log. Does anyone have any hints on what might be causing this dependency timeout issue?

Error message 'code': 'InternalFailureException', 'detailedMessage': 'Dependency Timeout'

And for some reasons, somehow this timeout issue disappears when the same scheduled process was run today, even though the pipeline and scripts stay the same (except the data in S3)