Bootstrap-Select needs double click to show options

I'm with a page where I have several forms. I'm using bootstrap select (v1.12.14) along with bootstrap 4.0.0 and java backend (with spring MVC).

The problem I have is that when I click on a select to show me the available options, you do not show them to me, but instead focus on the control, and if I click again, it shows me the options. The operation that I need is that with a single click it shows me the control options.

I add a select that I have echoed and it does not work

    Tipo remito:
        <select class="selectpicker">
          <option value="1">Entrega</option>
          <option value="2">devolución</option>
        </select>

Thank you very much, Regards