Small chance that the stem has bulged the steerer- even with the bolt removed the stem can be trapped.

might remove the bolt and attempt to tap the expander free- the bolt end shifted to one sides alternately a rod to insure no damage to the stem bolt.
if the expander is deemed free...
and still no success. Whacking the stem ear the bar clamp maybe with even something in the bar port and tightened up, to collapse the expanded portion of the stem.