yes. the Phone are located at the same site where the call manager is located. CUCM 9.1.2 with Cisco 7821 and 8941 phones.
The issue happen due the L3 core switch down/ or power outage for network. There is no issue with CUCM around 80 % of the phones get register automatically. but about 20% of the phone do not register automatically even if we leave for couple of days. The current work around is to reset the phone in order to get it register.
In that case i would start by checking for any switchport errors or ios related bugs for the switch. Additionally, if the issue can be replicated, then try capturing a sniffer from one of the switchports to which the affected phone is connected. This will provide details of the exact step in the registration process where the phone gets stuck , like if its failing to get dhcp info or tftp file or something else. I am aware of this kind of behavior on ATA's as there is a known bug for this, but not for the phone models specified by you. You may need to engage TAC if it requires extensive digging in.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.