Dull Finishing Or Unplated Fasteners

Because that is what happens.

Why not?

Automatic not set to shiny!

Improper process.

No process control.

Wrong/not enough/cheap chemicals.

No electric power.

The list is too long to go into detail here.

Hire a plater.

Polarity of the plating system is reversed. Instead of putting on the plating it is taking the base metal away.

Good Luck, Old Salt

Then why would the threads be so tight?

redthread-

Although a couple of contributors would tend to say I'm always wrong, I didn't see anything in the original question about tightening:

Why dull finishing or unplated fasteners after automatic electro plating ?

Using the reverse polarity will take the metal off the part just like the correct polarity will put the plating material in the solution onto the part.

Good Luck, Old Salt

Plating usually takes on the quality of the finish already there, if the metal was previously polished and shiny, all other things being equal, you mostly get a shiny finish after plating.....

Also, were the bolts plated with another metal in between, copper is sometimes used on steel/iron metals that corrode easily to "seal" the metal in, though my knowledge is sadly well out of date....

Plating is a science all on its own, an expert would take one look and tell you what is happening.....we here cannot do that quite so well!!

I think your vendor is not maintaining good quality control. You had breaking problem along with dull finishing problem. Just carryout chemical test and hardness test of fasteners and check if they confirm to specs. I suggest instead of electroplating you should try blackening process.