Incumbent Franklin Pierce was denied the Dem nomination in 1856. That’s it. There’s been speculation that LBJ might have lost the nomination to a Bobby Kennedy or someone else in ‘68 if he hadn’t bowed out.
Some others - Tyler, Fillmore, Arthur - were also denied renomination, but none of them was actually elected president. Tyler had been expelled by his party a few years before and Arthur didn’t put in much of an effort.