After 3 days trying to use the dcc.Loading, I gave up and opted for the second method described at the bottom of the page https://dash.plot.ly/loading-states, which works just great
I removed my dcc.Loading, and instead added the below css lines in my css file:
*[data-dash-is-loading="true"]{
visibility: hidden;
}
*[data-dash-is-loading="true"]::before{
content: "Loading...";
display: inline-block;
color: magenta;
visibility: visible;
}