I’m more familiar with my 3.6l than the v12’s, hopefully be someone with better expertise than I on V12 problems.
Has it been running ok until recently or is it the first time you have run for a while – i.e. been put away for winter months?
Good news is it starts! If it is relates to engine temp there are a few clues maybe. First is the engine temp sensor (different to temp gauge sensor) which inputs to ECU, giving cold start enrichment. They can go faulty and give incorrect resistance reading – or even the wiring connector gets corroded.
When it dies will it restart immediately or do you have to wait?