Charging cable difficult to plug in and unplug

Have you looked for any obstructions on the plug end or the receptacle end?
Have you looked at the contacts on the electrical connectors for corrosion/oxidation/etc.?

 

maybe some vasoline?

 

If you have the same problem when using a public charging station, then I would have the dealer inspect the connector on your Prime for damage.

Similarly, if you do not have the problem when using a public charging station, you should do a careful inspection of the J-1772 connector on your OEM charging cable.

Be aware that there is a locking mechanism on the Prime which can be set to prohibit the J-1772 connector from being removed from the car. Some of the Primes have a sensor which will not release the connector unless you have your key fob in your pocket. You should not be able to remove a locked connector, even with a lot of force, but you still should check that your Prime is not locking the charging cable and that the locking mechanism is not damaged.

(Also, I think the suggestion about using Vaseline was meant in jest. Getting grease on the metallic surfaces of the electrical connectors will prevent them from making a secure electrical connection and could result in your being unable to charge your Prime or your having the J-1772 connector overheat.)