The key bindings used by the review modes of org-fc conflict with some of the bindings used by evil mode.
As a workaround, you can add minor mode keymaps for each of the evil-mode states you're using org-fc with.
(evil-define-minor-mode-key '(normal insert emacs) 'org-fc-review-flip-mode (kbd "RET") 'org-fc-review-flip (kbd "n") 'org-fc-review-flip (kbd "s") 'org-fc-review-suspend-card (kbd "q") 'org-fc-review-quit) (evil-define-minor-mode-key '(normal insert emacs) 'org-fc-review-rate-mode (kbd "a") 'org-fc-review-rate-again (kbd "h") 'org-fc-review-rate-hard (kbd "g") 'org-fc-review-rate-good (kbd "e") 'org-fc-review-rate-easy (kbd "s") 'org-fc-review-suspend-card (kbd "q") 'org-fc-review-quit)