Good job repeating the talking point from the GAO memo. If you were paying attention in class, or ever did any business with the government, you would realize that people in the Executive Branch are responsible for doling out money from the "purse" and that they routinely exercise discretion in doing so.
If you didn't complete the job you can't expect to get the check. If the government finds out that you are, for example, a doctor filing false claims for medicare payments you don't get the check. The departments responsible for those kinds of efforts is in the Executive Branch.
Ask yourself a question. If Congress budgeted funds for a new police station in Mosul Iraq should the US government have sent the money to Mosul after it fell to ISIS? I think you know the answer is "no".
The Executive Branch has plenty of leeway to adjust the timing of payments, or even withhold them, based on its decisions that are taken as it implements the spending authorized by Congress.
Of course, and the examples you give are considered programmatic changes necessary in order for the Executive to implement the law.
The GAO found that in this instance that wasn't the case. They said the funds were withheld for policy reasons which is prohibited by the Impoundment Control Act.
We can say the ICA is bad, stupid or unconstitutional, but for now it's the law.
I can see that