Low oil level in hydro system
sticking linkages or valves.
Get a can of lithium spray grease and an air gun.
Clean all the linkages then give them a big squirt while working the levers.
Pay special attention the the neutral parking stops.
Wait till the grease dries out before you go mowing or it will pick up dust nd become abrasive.
Do not use WD 40. It is not a lubricant and will make wear in the linkages worse.