Return it to the factory for a free repair.
Note that removing material from the hammer is NOT a proper repair, and Colt may charge you for a new hammer.
In short, your gunsmith botched this up. This is a transfer-bar ignition system, and removing material from the hammer does NOTHING for increasing hammer strike or more reliable ignition.
Removing material from the hammer is a major safety violation in these type revolvers, and likely ruined the hammer.
These type Colt's have very thin case hardened surfaces with softer metal underneath.
This gives a part that will take shock, but have a super hard thin surface to prevent wear.
By "Taking off" the hammer face, it's likely he broke through the thin surface coat and destroyed the hammer.
In any event, as far as Colt is concerned, ANY alteration to a Colt hammer is cause to reject it and replace it with a new part.
These days, Rule One is: Never trust any local gunsmith with a Colt revolver.
Most locals do NOT know Colt's and often botch them up by "fixing" the WRONG thing.
If you're having ignition problems, the usual problem is either a mainspring, or a firing pin problem, NEVER a factory original hammer.
As a note: These later Colt guns have a firing pin that MUST, repeat MUST be replaced by the factory.
Replacement REQUIRES special presses and support jugs to remove and install a firing pin without damaging or even ruining the frame.
Allow a local to replace the firing pin, and the gun WILL be damaged, even if they tell you they have the right tooling., which 99.999% of the time they do NOT.