Regarding order is no longer accessible after being rejected

We do not know your application. That makes it a bit difficult to support ...

As Stefan notes, it is difficult to assist as we do not have any knowledge on your Project Management Tool.

However if you are talking generally about Appian task acceptance and rejection capabilities, there are no "issues" that I know of - aside from my users occasionally thinking they have submitted a "Reject" disposition to the business approval, where in essence by using the OOTB Reject feature they have only returned the task to the group it was initially assigned, minus the user who rejected, with no continuation of the workflow. 

More details on your question please.