I moved our Jenkins to a new server a few weeks ago and since it doesn't actually do anything, I gave the VM only few resources (the agents have the workload). This led to the main node being marked as offline, where it looked like this:

Finding the cause was a bit time consuming, which would actually be easy to fix:

• Within the table Nodes the icon has no tooltip (not like the icon within the build executor list)
• Disk space is too low. Only <0>GB left on <1>. (DiskSpaceMonitorDescriptor.DiskSpace.FreeSpaceTooLow) isn't this much helpful, as you don't know, how man disk space is required. So the test should also include the configured value of Free Space Threshold.
• As we running Jenkins already for years I didn't knew where I can change the settings, so I had to use a search machine. Node Monitoring sound more like sth. like Grafana or like Load statistics of a node. So maybe renaming it to Node Monitoring Settings would be useful
• Marking the node as Offline is rather confusing, as to me that sounds more like losing connection to the nodes. Defective would be better, but maybe someone has better ideas.
• An earlier warning would be useful. For example, if you fall below 20 GB, there is a warning that the disk is running low. And only at 10 GB the node is deactivated.