Withdrawing the H1B Extension Application

[chaitanya1015]

Can anyone please advise on the following scenario:

Initially, The employee's H-1B extension got approved till 08/31/2019 with Client A with Employer A and later employee got a new job with Client B and after joining with Client B he has filed for his H-1B Amendment with the same employer and got it approved till 3/27/2019 and the I94 that came with the amendment approval was valid until 04/07/2019. However, when the employee checked online, the i94 was valid until 08/31/2019 i.e until the initial H1B expiry date with Client A with the same employer.

That being said, the employee has filed for his H1B extension in regular processing with Client B with the same employer on 3/14/2019 and it's still under process. Now, since the employee got an offer with Client C and the start date is 04/22/2019.

Can the employee join Client C on 04/22/2019 and file for an Amendment + Extension with Client C with the same employer and once it gets approved, can the employer withdraw the H1B Extension petition that has been filed with Client B. Does this pose any immigration issue? (or) what other options do the employee have to pursue the new job at Client C. P.S: Employee is being employed by the same employer in all the cases. Any inputs are highly appreciated. Thanks .