Bootstrap modal not showning only on my machine

My problem is simple to understand: A bootstrap modal isn't showing when it's supposed to. As you can see in the image below, the website gets all greyed out, but it doesn't show the modal. The interesting thing is, this happens only on my machine. I've tried with Firefox, Chrome, Edge, also in Incognito mode, and nothing seems to have made a difference. However this works on anybody else's machine, including another one of my own. EDIT: I've tried clearing cache and using the option in the dev tools that use "no cache". Still nothing. The AJAX request returns 200, and I can see the modal HTML injected in the code, so I'd say it's working correctly.

Looking closely at the CSS with the dev tools, it seems that the .modal class still has a display:none attribute, and when I take that off, I can see the modal. But I shouldn't have to do that manually...

THis is the javascript that fires when you press the plus button:

    Start: function (id) {
    $.ajax({
        url: "/Progetti/ElencoProgetti/Create/", //this is the location of the modal
        data: {
            id: (id == null ? 0 : id),
        },
        success: function (data) {
            if (id == 0) {
                $("#nuovoProgettoLabel").html("Aggiungi progetto");
            } else {
                $("#nuovoProgettoLabel").html("Modifica progetto");
            }
            $("#nuovoProgettoBody").html(data);
            //NuovoProgetto.Init();
            $("#nuovoProgetto").modal('show');
        },
        error: function () {
            Swal.fire(
                'Evento',
                'Errore durante il caricamento',
                'error'
            );
        }
    });

THis is the HTML of where the modal will go:

<div class="modal fade" id="nuovoProgetto" tabindex="-1" role="dialog">
<div class="modal-dialog modal-lg" role="document">
    <div class="modal-content">
        <div class="modal-header">
            <h4 class="title" id="nuovoProgettoLabel">Evento</h4>
        </div>
        <div class="modal-body" id="nuovoProgettoBody"> 
        <!-- the JS injects the modal here-->
        </div>
        @*<div class="modal-footer">
                <button type="button" class="btn btn-primary">SAVE CHANGES</button>
                <button type="button" class="btn btn-danger" data-dismiss="modal">CLOSE</button>
            </div>*@
    </div>
</div>

Pretty sure JQuery version is 331. Not so sure on bootstrap version (the senior on this says major release is 4) I'm still fairly new at SO so if you need anything else please let me know. I'm at a loss... Even though I've provided you with what I think is sufficient code to understand this, you probably won't be able to reproduce the issue as it only happens on my laptop. Any clue as to what could produce this situation?