One of the things that happens is that many times the customer does NOT buy the OEM filter. If you try to use and aftermarket filter, they may not have the correct valve in it or the correct filtering size filter inside it.... this will cause the oil to fail to flow freely.
Make sure you are getting the CORRECT filter.
If that is not the problem, they there is a chance that the hydraulic cylinder may have taken that particular time to go bad. It may be bypassing fluid.
I did use a Kubota filter purchased from the dealer I bought the tractor from. The hydraulics were working fine until I changed the hydraulic oil.
OK on the filter.
Sometimes the hydraulics will quit for no apparent reason, though.
I am pretty sure that the problem is either in the hydraulic cylinder or the HYDRO itself.
There is a slight possibility that you are not getting enough oil into the cylinder and there may be air in the cylinder. You may have to take the lines off of the cylinder and physically put oil in the cylinder itself. then resemble and then bleed the system again as you have done before.
There is also a possibility that the section of the hydro that runs the hydraulic lift cylinder may have decided to go bad. The seals may have started to bypass oil or the motor portion of the pump may have finally given up.
These things many times will give NO WARNING at all before they go bad. It may be a coincidence that it happened just after you changed the oil.
Also when you changed the oil, you may have put a thinner oil in it than it had in it before. If you did NOT buy this unit brand new, then there is a possibility that the hydro was worn and whoever had it before you, changed the oil and put in a thicker oil to try to extend the life of the hydro.
One more thing that you can try, is to actuate the attachment lever back and forth many times and see if it will get better. Sometimes this will bleed the rest of the air out of it.