I’ve been using merlin-locate-in-new-window set to 'never for a while to prevent Merlin to open a new window.

Recently, it stopped working altogether, and it as far as I can tell, it is related to #1426.

I am not familiar enough with prefix argument, but the fact that this change breaks an existing configuration was a bit… annoying 😅. Fortunately, I’ve been able to recover my previous setup by defining my own helper around merlin-locate:

(defun +merlin-locate ()
    (interactive)
    ;; force `merlin-locate-in-new-window' to be 'never
    (merlin-locate '(4)))

I have a fairly customized Emacs configuration, but just calling M-x merlin-locate ignores merlin-locate-in-new-window, wihch looks like a bad UX to me.