The amount of times I've annoyed bosses about the worrying amount of warnings in projects that are in production, to then be completely shut down about my concerns is ... disheartening.
Where possible, get things in writing. Even if you have to do most of the writing yourself.
"Dear boss, please confirm that, as discussed this <time>, warnings A, B, C, etc. are not to be considered important and that we're pushing ahead." CC everyone on the team and maybe another boss or two if you dare. Wording it better than I have here is undoubtedly possible.
Then you can perhaps stall and work on other things until you get a response one way or the other.
And if that results in shitty boss behaviour or employment jeopardy you have a timestamped e-mail that you can point to as the beginning of the end.
Of course, if you really need the job and can't put yourself in that situation, instead document things for later. You can fire shots and warn customers on the way out rather than rocking the boat there and then.</time>