There is a little valve, called MLS valve which controls the speed of the 3pt arm movements. The switch, typically located under the seat opens and closes that valve. Closing the valve aperture reduces the flow rate of hydraulic fluid, until you can actually fully close that aperture, lock the 3pt arms and have no movements at all.
Since you had a backhoe on the tractor, it's common for some tractor owners to completely lock or restrict 3pt arm movements, so they don't interfere with backhoe operations. So maybe that is what's going on here. Either you turned the wrong switch, or the switch has become defective and no longer controls the valve.
I would double check hydraulic fluid levels first, and also reference your operators manual for the proper location of the 3pt arm control switch.
Just bought a 2019 Kioti CK3510 and am trying to adjust the MLS valve. From what I've found online, the jerky operation of raising the 3 point lifting
www.tractorbynet.com