Slime and Emacs 26.1

[Vladimir Sedach]

It can also be stale .elc files or something went wrong with loading
new files into the running Emacs if you updated packages after
upgrading to 26.1.

You can use FIND-FUNCTION to see the file Emacs last loaded a
function from. If you set LOAD-PREFER-NEWER to T in your init file
before loading any packages, Emacs will load the source file if the
corresponding byte-compiled file is older.

Deleting the SLIME .elc files, re-compiling the .el files (* . elc D
then * . el B in dired), and reloading Emacs will ensure that
everything is loaded correctly.

Vladimir