It is an existing limitation in design of netdump.
When PSOD happens in DF/NMI/MCE contexts, netdump cannot work even though it has be configured. The warning message logged on PSOD screen:
"Cannot continue NetDump from DF/NMI/MCE stack."
And then coredump switches to disk/file dump automatically. If no disk/file dump configured, user may see more warning messages:
"No place on disk to dump data."
"No file configured to dump data."
This is by design
Use local disk dump or file dump.