We found the reason why it happens this way.
The DataTable component contains tiny classes content/footer/toolbar/etc. along with much specific such as: bl-data-table-toolbar.
And in your app, there is an app extension (styles/css) that has .content class which affects the component.
I’ve created an internal ticket to fix it BKNDLSS-26359.
But, until it’s done in your styles need to specify the .content class like that: .content:not(.fake-data-table-content), I believe it can be removed tomorrow.