Endless "Invalid face attribute :background nil" when using Centaur tabs

In #25 (closed) you implemented support for the Centaur tabs package. In principle it works fine. However, if I enable both Centaur tabs and either of the two Modus themes, my *Messages* buffer gets a lot of the following messages:

Invalid face attribute :background nil [52 times]

It seems that every key press leads to three of these warnings and every "step' of my mouse scroll wheel leads to an increase of two.

This is the simplest Modus config I used to try and diagnose this:

(use-package modus-themes
  :init
  (modus-themes-load-themes)
  :config
  (modus-themes-load-vivendi)
  )

And this is the simplest Centaur tabs config:

(use-package centaur-tabs
  :demand
  :config
  (centaur-tabs-mode t)
  :bind
  ("C-<prior>" . centaur-tabs-backward)
  ("C-<next>" . centaur-tabs-forward)
  )