The piston froze partially open while splitting a log and now it wont go forward or retract

sounds like when you move the lever to retract, the valve to allow the oil from in front of the piston is not opening to allow the cylinder to retract under pressure
could be that , a failing hose internally acting as a blockage or if fitted a flow valve that is shutting off the return flow
take it to a hydraulic shop and have it checked out

Try opening the brake bleeder. Some foreign models have a screw in the rear of the caliper that retracts the piston.

The driver will not retract if the driver is bent, piston oring too loose or too tight or the check band is loose or missing. Easy test, remove air and push the piston to top of cylinder. It should move up with very little effort. If hard to push, oring too tight or driver bent. If piston moves too easily and drops back down under its own weigth, oring too loose. If easy to push and stays suspect check band (check band is located on the outer lower part of the cylinder. Looks like black rubber band or series of orings that fit over series of holes. ). If the band is split or broken, replace with series of orings to cover all holes, or use any rubber like bicycle tube. Good luck with your repair.

front calipers pistons straight in with c-clamp or piston retracting tool
rear calipers piston may need turning to retract should be provision
in piston face to install tool needed to performed work
tool is small square box with multi face that will service most calipers

open the bleeder on the brake caliper, if you can then retract the piston then replace the brake hose that aitches to the caliper if after you open the bleeder you still can not retract the caliper piston then you will need to replace the caliper.....GOOD LUCK

could be a jammed nail in the nose/magazine area or a driver problem. is the driver fully retracted or stuck partially down in the nose. UNPLUG the air before checking. If the driver is partially down I would think a jam and fully retracted you might have an issue with the piston/driver assembly.

No, sounds like just one of your pistons is frozen. Incase you haven't done this yet, also fyi, you have to collapse both pistons at the same time. Try placing a strip of wood across both pistons and squeeze them both at the same time with your C-clamp. If one is hung up, this may free it up, or even it out so it fits back in the caliper properly. Or, I don't know if you didn't know this about both pistons, but if you squeeze only one, all the fluid will push across to the other and push it out, causing it to partially come out and be crooked in the caliper. Good luck!!

I beleive there is an hydraulic release valve that must be in the open position for this to retract

this could be one that twist to go back in this is most likely the case. the tool will help check the local parts store tool might be a better price.

Use a "C" clamp slowly to push piston in. If not available push hard in center of piston with a wooden hammer handle or similar. If still won't move, crack open bleeder screw and try. Double check after re-install & make sure it retracts properly in case seized or partially seized.