Assuming no physical damage, pressure is the problem.
Don't do as so many will and use a hammer to beat the center prong of the male connector.
Saw a shopbuilt jigger: C-clamp with the bottom pad cut off and a split-in-half-lengthways socket welded in its place. Open the clamp, slip the half-socket around the hose fitting hex and screw the clamp down to gently push in the male-end prong. Easy. Just a tiny spurt is all it takes to relieve pressure so you can hook uip.
When sitting the implement down for removal always (only way I know to reliably do so) shut down the engine and wobble the stick in all directions to fully relieve all pressure just before disconnecting hoses. Makes hookup easy later.
I carry a spray can of engine starter fluid (aka ether) in toolbox. Never in Kubota engine but is handy to spray-clean hydraulic connectors---good strong blast and no residue.