MTurk sandbox showing "There are no more of these HITs available" message before user has completed all HITs in a group

Hello, our team is working on testing a group of 6 HITs that we have published on the sandbox, but some workers are only able to complete 2 of the HITs in the group before receiving the message mentioned in the title of this post. After receiving this message they get the same message when trying to complete any other HITs that we publish. We also have team members who have been able to complete all 6 HITs without issue. There are not qualifications set on the HIT and the max number of assignments is much higher than the number of assignments completed before this issue occurred. Any help on this situation would be greatly appreciated!