Cisco 8821 looses registration continuously

[RocioRamirez]

 We acquired 8821 phones but their performance is lousy, after configuring and delivering them to the end user they report that the phone does not work, the phone is connected to the wireless network but it is not registered, we have to restart the phone so that it can be registered but everyone The same thing happens to them every day. We have AP meraki MR52 with excellent coverage, the CUCM version is System version: 11.5.1.10000-6 and Cisco 8821 frmware is sip8821.11-0-3SR6-15

[George Sotiropoulos]

Hello @RocioRamirez ,

Please check if the phone looses WLAN connectivity when the issue appears, meanwhile. you may try the following:

https://community.cisco.com/t5/ip-telephony-and-phones/cisco-8821-wriless-phone-not-registering-with-cucm/td-p/4020522

George

[Leo Laohoo]

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@RocioRamirez wrote:

after configuring and delivering them to the end user they report that the phone does not work

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Does this mean that when the phone is waiting to be delivered the performance of the phone is better? 
Before the phone is being shipped OUT is the phone turned on or off?

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@RocioRamirez wrote:

we have to restart the phone so that it can be registered but everyone The same thing happens to them every day.

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Everyday, right?  Is the problem worst when the phone is sitting on the dock (and charging) or when being used?

[RocioRamirez]

The phones are connected to a 5 Ghz network, but I have detected that when the user enters an area without coverage for obvious reasons, they disconnect and when they reconnect to the wireless network the phone no longer registers in the CCUM until we reboot, this happens with all phones. attached the event log of one of the phones and status messages

This is records of one of the events that we had 18:49 the phone was connected 18:49 - 18:51 loses coverage and connection 18:51 is reconnected but no longer registered

[Leo Laohoo]

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@RocioRamirez wrote:

but I have detected that when the user enters an area without coverage for obvious reasons, they disconnect and when they reconnect to the wireless network the phone no longer registers in the CCUM

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This is the information I was afraid of.  
Read the Release Notes for the different firmware version for the 8821 and there are a lot of out-of-range (aka OoR) bugs.  In essence, when BEFORE the phone leaves WiFi coverage, TURN OFF THE PHONE.  If the phone isn't turned off and leaves WiFi coverage, the wireless NIC of the phone simply goes "bat$hit crazy" and crashes.   One example is CSCvn81608.
This has been a very well-known issue with the phones and over how many firmware releases the behaviour still has not yet been fixed.