Not sure if you tried retracting all jacks first but you should do that and then turn system off and back on and again retry leveling. If that does not correct the issue, then you have a fault code on that jack that will have to be diagnosed and possibly repaired or just cleared before normal operation can be restored. Let us know what you find.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7