Thanks, Kim.
I decided to troubleshoot more strategically, after posting, and start narrowing down whether the issue is in the computer, switch, network, or device.
I installed DADman on the RMU (Mac), which has never had DADman installed on it before, and the device connected right away.
Once connected, it began functioning normally again and has remained stable since.
I’d still like to figure out what the issue is, but at least I know it’s an issue between DADman and the PC.