The project would cover areas of Yucatán state, with the tender expected to be launched in December when the incoming government takes office.
A consortium of Uruguayan, Spanish and French firms allege that its score in the evaluation process should have been higher. The process has already been stalled after to a challenge by competitor Acciona.
Spanish banking giant BBVA said it has "expressed its willingness to negotiate with the Bolivian government to produce a smooth and orderly transfer with the regulator and the authorities."
The Brazilian development bank saw large H1 gains from the sale of shares in certain companies and improved loan book quality allowed it to reduce loan loss provisions.
Although construction of the rail line is said to have advanced around 78% ready, according to official information, media reports and observers believe it unlikely that the project will be completed before the end of President Enrique Peña Nieto's term in December.
The previous government left the final economic approval of the project in the hands of the new government.