I posted this reply previously to someone who was having a similar(I think)problem,anyway it might be worth a look.Could be that it doesn't re-engage after several hi-lo shifts.
My Dk40 had that problem.My tractor has a creeper gear so I have two levers.The levers are so long that they have too much spring in them.
I noticed that on the optional gear lever Kioti had welded a little stifftener to the lever so I did the same to the hi-lo lever and it shifts like a charm.That was two years ago and it still works great.
Have someone move the lever while you observe it from below,if you see it flexing that is where you want to ad a little backbone to the lever....Mike.