The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.
In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.
A properly functioning 3750X stack, functional behavior shouldn't vary just depending on which stack member you connect to.
What IOS version is being used?
Is there any difference at the configuration between this problem ports and ports that works well? Does another devices works well at this ports? Is there any errors at this ports?
Both your Gi3/0/21 and Gi3/0/24 ports have hardcoded speed and duplex. Can you please configure both to "auto" and see if there is any progress.
Well, the last test that I can to offer is to put another device (not a phone) to this port and look how good it works. If there is problems as well than there could be damaged ports. If not than it's better to contact TAC if you (or your client) has a SmartNet contract.
Well... I don't think, Allert, because I before I had done test connecting the ip phone on the switch 1 of the stack they recorded normally. I'm arriving at the conclusion that switch problem ....