It is possible that USCIS has approved the H1B for only one month based on documentation and/or project. This H1B petition may have been filed several months ago (Under Normal processing) and when it was approved, it was approved only until 07/21/2017. What is your basis to claim that it is an error, if it was not a service error, you may be out-of-status since 07/21/2017.
Your Employer or Attorney must contact USCIS immediately to get the actual approval dates vs service error.
Example: H1B Was applied on 01/05/2017 and was approved on 06/13/2017, USCIS may put a start date of 6/13/2017 although you may be legally eligible to work from 01/05/2017 under H1B portability regulations.