Mexican actor and YouTuber Alan Estrada was on board the Titan last year when it lost communications at around a depth of 1,000m, which led the crew to almost abort the mission.
Mr Estrada filmed the expedition and told the Reuters news agency that just as they were aborting the mission, communications were recovered and the sub was able to make the descent.
Follow our live coverage of the missing sub here, as the search is being expanded to cover twice the size of the US state of Connecticut.
The US Coast Guard has vowed it remains a search and rescue operation, saying: “We have to remain optimistic and hopeful”.
Contact with the sub – which has five people on board – was lost on Sunday as it made a descent to the Titanic wreck.