It could be damaged, but that would show if you check the resistance. More likely it's a mechanical issue, or a bad connector, etc

The electromagnetic field strength is proportional to the number of coil windings. The copper wire in a coil has a thin film of insulation on it. If the coil has been stressed and overheated, it can melt the insulation and numerous windings become bonded together, effectively reducing the number, and thereby the magnetic strength. Also, a reduction of voltage to that coil will have the same affect, which can occur through oxidized connectors. You can test this by running a jumper wire directly from power source to the coil and see if the strength improves.

Also as the previous poster mentioned, the coil sleeve could be worn or melted causing restriction and an apparent loss of strength.

Not sure how you're monitoring that, but the DC voltage supply in most games is unregulated, so you'll always see a higher floating voltage with no load, but lower when a coil is energized....any coil. But if you're seeing a larger voltage drop with that coil compared to others, then I'd be looking at bad connectors and the coil.

What is the coil for? If it's a flipper coil, the problem could be the EOS switch or flipper button switch giving you resistance. If it is something else, it could be a number of different things. Have you had the mechanism apart and inspected the sleeve, plunger, and stop yet? Pictures of all of that would be good for us to see, if further diagnosis is needed.

I had a “weak coil” in my Bride of Pinbot under Playfield kicker. Turned out the sleeve was just really dirty and for a price of .69, I was able to return to normal power.