fails with *too-deep* on fresh install (Spacemacs)

[clembu]

Using spacemacs develop.
Excluded spaceline from loaded packages, and added this in a custom layer:

(setq display-packages
      '(smart-mode-line))

(defun display/init-smart-mode-line ()
  (use-package smart-mode-line
    :ensure t
    :init
    (sml/setup)))

Even when just doing this without any layer setup and just manually calling sml/setup, I get the result you see above: the modeline is just *too-deep*

SML version is 2.13