Need help debugging GNUS problem

[rprospero@gmail.com]

I recently tried to set up mail splitting in GNUS.  Instead, I am now in
a position where I cannot access any of my e-mail.  Furthermore, my
usual debugging strategy of starting at "emacs -Q" and working through
my init file from there isn't working, since the problem still occurs
even without my init file.

To be more specific, when I load GNUS, all of my groups appear.
However, if I attempt to load any of my maildir accounts, I get the
following error

--------------------------------------------------------------------------------
Debugger entered--Lisp error: (error "Trying to require a method that doesn’t exist")
  signal(error ("Trying to require a method that doesn’t exist"))
  error("Trying to require a method that doesn't exist")
  gnus-get-function((nil "") server-opened)
  gnus-server-opened((nil ""))
  gnus-check-server((nil ""))
  gnus-select-newsgroup("nnmaildir+Professional:INBOX" nil nil)
  gnus-summary-read-group-1("nnmaildir+Professional:INBOX" nil t nil nil nil)
  gnus-summary-read-group("nnmaildir+Professional:INBOX" nil t nil nil nil nil)
  gnus-group-read-group(nil t)
  gnus-group-select-group(nil)
  funcall-interactively(gnus-group-select-group nil)
  call-interactively(gnus-group-select-group nil nil)
  command-execute(gnus-group-select-group)
--------------------------------------------------------------------------------

With "Professional:INBOX" being the group that I attempted to load in
that example.

I've confirmed that all of my e-mail is still in the
Maildir and accessible through other mail apps.

Any advice on where to start looking to fix this issue? I'm on version
25.3.1 and running on the Nixos distro.