Hi @tnielsen2
The neighbor is removed only at the next discovery process, which means you should get the alert between the issue and the discovery.
But at discovery time, only the online neighbors can be known. Unlike BGP, there is no neighbor definition in OSPF, most of the time, multicast hellos are used:
There is basically no way for the network device to know if a neighbor disappeared on purpose or if it is an issue/incident. And LibreNMS polls the device, so LibreNMS has no way to determine if it is an issue or a normal device turned off and removed from network.