We had the same problem on our 2014. 2100 (no slide) after only a year or so. The problem is corrosion inside the switch, Turning the plunger makes you feel better but has no effect, Adjusting the plunger moves the contact surface to a cleaner area but is only a temporary solution. Eventually the corrosion will move to the 'clean' area of the contacts.
I got a new switch from Kermit and installed it and covered the exposed switch and wires with a healthy dose of spray 'flex-seal'. No problem since then - 4 years plus, Took the old switch apart and cleaned the contacts and carry it as a spare. - although it would be messy to replace it through all of the 'flex-seal.