RegEx parsing of cmdline fails if argument contains "_"

[DGRFL]

Following yaml is used to extract arguments Cell / Node / Server from a Websphere App Server commandline.
`
process_names:

• name: "{{ .Matches.cell }}:{{ .Matches.node }}:{{ .Matches.server }}"
  cmdline:
  • '-Dosgi.configuration.area=/apps/profiles/(?P(?P[A-Za-z0-9]+)Node[0-9]+)/servers/(?P[^/]+)/configuration'
    `
    is matching for "nodeagent" "msg1" but not for "bsSN_DC1_1".
    When testing on regex101.com, there is a match and "server" is extracted.

I tried replacing
/(?P[^/]+)/
with
/(?P[A-Za-z0-9_]+)/
But no success.
ANy idea?