Lexus LX470



My 2002 LX470 developed starting problems about 4 years ago. It cranks but won’t start. It does it about once a year and is not related to weather(has done it in the summer and winter, wet and dry). Each time I have had it flat bedded to the dealer , when they take it off the truck it starts, so the dealer has never been able to diagnose the problem. Any ideas?