Hey @gvallverdu
Looks like the problem is that DataTable uses a CSS class called row for styling the table, which clashes with Bootstrap’s row class. Specifically I think the problem is that Bootstrap’s row class sets flex-wrap: wrap.
I tried your example and managed to fix the odd layout by adding the following CSS to my assets folder. Let me know if it works for you.
.dash-spreadsheet .row {
flex-wrap: nowrap;
}