Sounds like the Marlin 336 ejector (the little angle spring that slides into the side of the receiver) may have come loose and that tends to jam up the works.
If you move the lever forward with the ejector out of its slot, the lever jams in the open position because the ejector jams the bolt/firing pin assembly.
If the ejector wasn't fitted in the little hole on the left side of the receiver, it can slide around and come loose.
I speak from experience. I had it happen the first time I cleaned the rifle.
Now I am very careful to get it back into the little hole, before I slide the bolt in place and reattach the lever.
You can check to see if that is the problem. If there is someing in the hole flush with the exterior of the receiver, then the ejector is in place. If there isn't anything in the hole or the pin is not flush with the receiver then it probably has come loose.