FWIW. Ran into a similar issue whereby I was querying a database on every autocomplete keyup event to refresh the data list. Discovered that every call to mdbAutocomplete added another DOM UL, plus discovered a need to perform a blur and focus on the autocomplete field in order to trigger the drop down list to show. The code I settled on...

  const autoCompleteId = $( 'autoCompleteId' );
  autoCompleteId.keyup( event => {

    let result = SQL.select( ... // SQL select based on autoCompleteId.val()

    // Remove the old drop downs.
    autoCompleteId.siblings('ul').remove();

    // Generate the new list.
    autoCompleteId.mdbAutocomplete({
      data: result.map( row => row.lastName ),
      visibleOptions: 7
    });

    // Trigger autocomplete to show the drop down.
    autoCompleteId.blur();
    autoCompleteId.focus();
  } );

It took some time to figure this out through trial and error, so hope this helps someone else.