I am not at all familiar with that particular pistol, but this can’t possibly be right.
Just a wild guess, but I’m wondering if the firing pin safety is not properly disengaging when the pistol is being fired single action, but is disengaging when fired double action.
If you want to, try this with an unloaded pistol:
Point the pistol straight up and drop a pencil in the barrel, eraser first. Pull the double action trigger (causing the hammer to cock and then fall) and hold the trigger back – presumably the pencil will be propelled out the barrel by the firing pin strike.
Still holding the trigger back, cycle the slide to simulate loading a fresh round. Then release the trigger, which should now put you in single action mode (hammer cocked). Replace the pencil and pull the trigger – the pencil should again be propelled out the barrel.
If the pencil isn’t propelled out, the firing pin isn’t hitting it. You then need to figure out why.
Ultimately, though, I think the pistol is going to have to go back to Ruger.