Device disconnects do not always indicate a disruption for end user connectivity
When a device shows disconnected in UniFi Network it does not necessarily mean that users connected to that device experienced an internet connectivity disruption. In the case of a power outage or ISP outage it's likely the users did experience a connectivity disruption. But in other instances like a communication issue between the device and server or server and device, the device may show as disconnected or offline in the UniFi Network application but users are still connected to the internet without interruption.
Common causes
Power outage
ISP outage
Connectivity issue between the device and the server
Connectivity issue between the server and the device
How to determine which is the cause of a disconnected UniFi device
If uptime on the device is low it’s probably a power issue
If only one or a few devices in one site disconnected, it’s probably a connectivity issue between the device and the server
If all devices in one site or a couple sites which are geographically close or using the same ISP then probably ISP outage
If all devices disconnected at the same time across all sites, it’s probably a server issue or connectivity issue between the server and device
Resolving problems
For a power issue, check the power source and consider implementing a uninterruptible power supply or redundant power configuration.
For a connectivity issue between device and server, check the cable and the uplinks between the device and the internet. You can also check to make sure DHCP and DNS is configured and working. Make sure the firewall has not blocked the connection to the server or categorized it as malware.
For ISP outage, contact the internet service provider
For a server or connectivity issue between the UniFi Network server and devices contact HostiFi support