Your slime installation is broken / is in multiple places.

On Tue, Feb 19, 2019 at 1:21 PM Jim Newton <jimka.issy@gmail.com> wrote:
Since upgrading to emacs 26.1 (because emacs 25 has problems with pegging the cpu on mac), I get some weird problems with slime.      Is anyone else using slime with emacs 26.1?

Here is an example problem I have.

Debugger entered--Lisp error: (void-function slime-changelog-date)
  slime-changelog-date()
  slime-startup-message()
  slime-repl-update-banner()
  slime-init-output-buffer(#<process SLIME Lisp>)
  slime-repl-connected-hook-function()
  run-hooks(slime-connected-hook)
  slime-set-connection-info( ... stuff deleted ....)

But when I look in the function slime-startup-message, there is no mention of slime-changelog-date.

(defun slime-startup-message ()
  (when slime-header-line-p
    (setq header-line-format 
          (format "%s  Port: %s  Pid: %s"
                  (slime-lisp-implementation-type)
                  (slime-connection-port (slime-connection))
                  (slime-pid))))
  (when (zerop (buffer-size))
    (let ((welcome (concat "; SLIME " slime-version)))
      (if slime-startup-animation
          (animate-string welcome 0 0) 
        (insert welcome)))))