When submitting bug reports, to better narrow down where exactly the problem is, it is generally best to try and control for unnecessary variables - in this case, configuration that isn’t needed to reproduce a problem. For almost all of my bug reports, I use the below config, either as-is, or to then tack on to it whatever mode-specific configuration or whatnot I am trying to debug. Most of this minimal config is to adjust irritating defaults. Enjoy!
(in-package #:nyxt-user)
(define-configuration browser
((restore-session-on-startup-p nil)))
(define-configuration buffer
((default-modes `(nyxt/emacs-mode:emacs-mode ,@%slot-value%))))
(define-configuration document-buffer
((search-always-auto-complete-p nil)))
(define-configuration web-buffer
((default-modes `(nyxt/blocker-mode:blocker-mode ,@%slot-value%))))