Delete mu4e-company.el. Turns out that mu4e has built in completion.

load.d/mu4e-company.el

@@ -1,15 +0,0 @@
-(defun mu4e-company-contacts (command &optional input &rest ignored)
-  (interactive (list 'interactive))
-  (cl-case command
-    (interactive (company-begin-backend 'mu4e-contacts-company))
-    (prefix
-     (when (eq major-mode 'mu4e-compose-mode)
-       (save-excursion
-         (beginning-of-line)
-         (if (and (eq (line-number-at-pos) 2)
-                  (looking-at "^To: *\\(.*?\\)$"))
-             (match-string-no-properties 1)
-           'stop))))
-    (candidates
-     (--filter (string-match-p (downcase input) (downcase it))
-               mu4e~contacts-for-completion))))