Cant resume on hold calls in cucm 9.1

I am a telecom/network administrator for a bank.  Lately I have been having users complaining that often when they put a user on hold to either check on something or to transfer them, they cant resume the call.  They hit the resume button but the phone does not respond. This is happening on at least 5 phone in the same branch. Please let me know if I can provide any further information.
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José MéndezCommented:
Sounds like a known bug CSCun26289. Look it up here

Check if the affected phones run 9.3(1) firmware and upgrade to 9.4 if so.

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JobeethemageAuthor Commented:
I will try this either Monday or Tuesday and get back with you on it.
JobeethemageAuthor Commented:
I am going to upgrade the firmware hopefully today and will comment back.  I welcome any other comments or suggestions.
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José MéndezCommented:
You can always try unplugging the headset piece and do a conference to see if it matches the bug conditions.
JobeethemageAuthor Commented:
They use headsets at this location.   In order to update firmware on just a couple of phone, do I need to load the new firmware in cucm and then just reset the two phones or is there an easier way to just update 2 phones?
José MéndezCommented:
This guide explains how to upgrade the firmware on just 1 or 2 phones, disregard the topic about the Auth Fail error
JobeethemageAuthor Commented:
My earlier post was wrong. I meant to say they don't use headsets at this location.  Just wanted to clarify that.
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