Not long ago, I had a contactor problem on a Manitowoc rooftop condensing unit. The control circuit is 208 volts, fed from the line side of the contactor, and a low pressure switch is used for de-energizing the contactor when the unit pumps down due to a closed solenoid down in the ice maker head.
The low pressure switch contacts started to cause a chattering, then each time the contacts closed, the high compressor starting current pulled the voltage down which made the chattering even worse. Because the voltage drop was different each time the pressure switch operated, the unit could be making ice normally for up to a week or two.
The fix was to replace the damaged contactor and the pressure switch.
In this instance, the fact that line voltage was used for the control circuit was a key element in the problem, and it was difficult to find the cause because the switch did not always behave in the same way.
Had something similar on a wif freezer last week. Happened to catch it in the act. Was checking between L2 and T2 at the time and was getting a sporadic voltage drop. Quickly went back to the disconnect and had it there. Disconnect wasn't always making good contact. It was at a restaurant and every time they loaded the freezer they shut it at the disconnect. Changed it out and gave them a pump down switch.