Priority scanning requires SNMP write access to properly work. The first step in this case is to verify that the device actually has DCE assigned within the "Current ASISubscriber" in the [SecureInterface] section within the config.ini file for the device. For information on how to pull the config.ini file, see knowledge base FA156131.
; APC Secure Interface (ASI):
; To add an ASI trap recipient, list the IP address in the following form:
; <ip address>:<port>, <subscriber type>
; To remove an ASI trap recipient, list the IP or DNS name using the keyword:
; To remove all ASI trap recipients, use the keyword, value pair:
; To change the Authentication Phrase, or the Encryption Phrase,
; use the AuthenticationPhrase, EncryptionPhrase keywords respectively.
; i.e., AuthenticationPhrase=ASI auth phrase
CurrentASISubscriber=10.10.10.10, ISX Manager
Please note that DCE must set this value using SNMPwrite, so ensure that the SNMPwrite community string within the "SNMP Device Communication Settings > Device Scan Settings" matches an SNMP community string on the device with Write or Write+ access level. If DCE is unable to write to the device, you should see that there is an unauthorized user attempting to access SNMP interface within device event log, as long as it is not blocked on the network. This write of the DCE IP to CurrentASISubscriber should occur about every hour.
If this does not correct the issue, you will likely need to work through local escalation in order to run a packet capture to view packets for the time frame DCE should have received the alarm instance trap that the device should send when an alarm occurs.