It could be lubrication, but probably not.

It could be an improperly fit cylinder stop, or the cam surface could be rough from filing during fitting.

If the gun was used when you bought it, or if you have changed or cut the rebound spring, either a shortened spring or a too light spring is a good possibility.

Finally, if it functions properly when the trigger is released normally, just relax and let the trigger go forward, then it is very likely that this is what is referred to as an "Operator induced malfunction". Quit riding the trigger and preventing it from recovering normally. If the trigger feels a bit "lazy" on recovery then replace the rebound spring with a new factory spring.

Other possibilities are an improperly fit rebound slide that isn't rebounding the hammer sufficiently the allow the hammer block to rise freely between the face of the hammer and the surface it strikes on the frame. It could also be a defective or damaged hammer block. There may also be metal chips, either from the factory, particles of brass, sand, etc. inside the gun causing any number of problems. Start by watching your finger, giving the lockwork a good cleaning and lubrication and see what happens from there.

In over 50 years of working on S&W revolvers I have seen every one of the above reasons for a trigger not recovering positively.