I've made a couple of posts about my K22 made in 1957. Works great in double action but hangs in single action. Took the side plate off and cleaned and lubed it and then it still exhibited the "hanging thing" in single action. Lastly I took it out a week or so ago and I fired it, my buddy fired it and his son fired it and it never acted up, all of us shot it in single action mode. So did it just need shooting or what? I'm mystified.
Sounds like it could have been something as simple as a tiny crumb of grime or milling debris in the wrong place, and it finally worked its way out or was ground down to a point where it no longer mattered.
I think this is just a "moving parts" situation. Sometimes a piece of machinery needs to be cycled a few hundred times before the surfaces all work together properly.
What Dave said....all too often folks ask "why or what" and its hard to tell without the gun sitting in front of you, to make a PROPER & CORRECT evaluation or remedy...........so simply clean & oil and try again...stuff 'sits", old oil gums up and makes thinks sticky, parts NOT able to move as they are intended...glad it worked out for you......