I just put on a Landpride grapple on my BX25 with a 3rd function valve kit. The grapple opens and closes 2 to 3 times and then the hydraulics freeze. After some effort I remove the hydraulic lines - relieve the pressure from one of the lines - reconnect and again after 2 to 3 openings - it freezes.
Its possible that you have the hoses reversed,
actually its most likely the cause as the oil is only
supposed to flow through the third valve to the function
and then back to the tank.
Is your loader equipped the the single stick gimbal control
for the bucket tilt and loader raise and lower function?
You will probably be better off using the rear remotes if you have a free pair as the gimballed loader valves are not the greatest things to use for loader mounted attachments as these valves wear and the gimbal control springs weaken.