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In an interview with James Cameron, he mentions[1] that he and other submersible industry experts believe that they did in fact have warning, as they had dropped the weights (which were found far away from the debris field) and were attempting to resurface before the implosion:

[1]: "This Oceangate sub had sensors on the inside of the hull to give them a warning when it was starting to crack [...] they probably had warning that their hull was starting to delaminate. [...] It's our belief - as we understand from inside the community - that they had dropped their ascent weights and they were coming up trying to manage an emergency." https://youtu.be/rThZLhNF_xg?t=472