There is also a post on KMS with another solution, document ID AL395
Title53xx sets are stuck at Application loading reported after upgrading to MIVB version 9.2.0.59
DetailsMitel Support has been investigating reports that some 53xx/53xxe are stuck at "Application Loading" post upgrade to MIVB 9.2.0.59. The sets work fine but the Application Loading is preventing the key labels to download.
Current investigation has confirmed that this was due to the Firewall rules containing a policy for port 3998, This had resulted in any 53xx and 53xxe sets behind those firewalls from being able to download the button labels. (SAC Database).
PBX logs will become overwritten with the following log once a phone is stuck that is not allowing the port 3998 to fully respond between the PBX and the Minet phone;
474 WARNING 2021/10/27 15:31:22:340 Main SAC 9741 10.100.2.10 Software SwitchAppComms.cpp(2242)
SacDevCommsServer->AcceptCount (
not less than MAX_CONCURRENT_ACCEPTS (
Root Cause: As of MIVB 9.2, port 3999 (unsecure) is no longer accessible and port 3998 (secure) will exclusively be used for application communication between the MIVB and supported Minet sets.
Note1:this will affect both 53xx and 53xxe sets.
Solution:Confirm Firewall configurations to allow port 3998 to ensure continued operation of connected sets, failure to do so may cause 53xx sets not to be able to load their keys and get stuck at