const selectEl = document.getElementById('mySelect');
const select = new mdb.Select(selectEl);

creates a always a duplicate of the specific select element.

We use the umd and variant. In order to rule out the possibility that we have an error somewhere in our own code, we have set up a minimal page that only loads the mdb scripts and contains a select field. The error is obviously in the framework. I remember that select always caused trouble in the old versions, too. At the time, the select had to be destroyed beforehand and reactivated after setting the value. This is obviously no longer possible in the new version.