Recent activities by the Soviet government concerning a statewide conspiracy to dope their Olympic athletes, only adds fuel to the fire that perhaps they also covered up a failed space exploration. The credibility of the Soviet Union has been tarnished, and I don't believe covering up a failed space exploration is out of the realm of possibility, either.
In 1959, Isaac Asimov highlighted the suspicious lack of reported failed missions from the Soviet Union. He argued that the only way the Soviets could have such a high success rate was if they were using time-travel to abort launches that would fail. There is a much more reasonable alternative: that failed missions were simply not reported. Indeed, the United States space program, as of 1967, had cost the lives of eight astronauts, and was widely hailed for its adherence to somewhat obsessive safety measures. The Soviet program, which was known to place less emphasis on cosmonauts and safety in general, reported the loss of only one life. The soviet emphasis on the risks of manned space exploration is unlikely to have stemmed form this single incident. Therefore, we must accept that the Soviet Union must have hidden space exploration records, or concede Asimov's absurd suggestion.
It appears that the Soviet Union may have covered up a failed space exploration. It is not beyond the scope of the Soviet Union to do so, and based on their past history of trying to cover up embarrassing mistakes, it is not at all unbelievable that they would have done so.
No government is going to admit to a mistake if they can get away with covering it up instead. The Soviet Union is led by a well-known megomaniac and it certainly would not serve Putin's purposes to admit to failure of any kind. This specific event was probably not the first of its kind either. There are rumors about bases on both the moon and Mars. How are we to know truth from fiction?