Prolog: Unhandled exception: pce(object) `@prolog_warnings/emacs_hit_list' does not exist

Question

I wrote some days ago about a problem with imported_procedures and I was thinking turning off autoloading of libraries. So I used the command :- set_prolog_flag(autoload, false). and now I receive this error:

Unhandled exception: pce(object) `@prolog_warnings/emacs_hit_list' does not exist

I don't even know what this error is: I tried to search online emacs_hit_list for an answer but I didn't find anything. What should I do?

In case you're wondering what I'm using: I'm using SWI-Prolog 8.2.1. The code that generates the error is this:

vertices(G, Vs) :-
   findall(V, vertex(G, V), Vs).

Thanks in advance!