Did you paste the codes into the Volume + Hard Button on the System Page? If so, in the device that is having problems, go to the Device Properties and ensure that on Volume +, you have not chosen to override the System Page Volume + there (i.e. Punch-Thru is active).

Another thing to try. Does the code work if put on a button on a page in your configuration?

Please paste the original code you tried here so we can be sure on same page. Also, have a look at changing the 'Duration' of the IR Code.

Reason I am asking for the code is because I cannot locate Volume +/- in the Thread linked above.