Larry's right. Although it hasn't been an issue on our Beaver, it was on our old Pace Arrow once. Make sure the door magnetic contacts haven't obviously gone askew from one another and no longer align (unlikely), then see if you can see and check the one (jam side) with wire connections in back and that they're secure. You might test operation by trying to trigger the switch with a handheld magnet, rotating it to get the polarity right.
Our entry doors are subject to more "abuse" than many other coach parts, with often unintentional slamming (grandkids, wind gusts), etc. Windows loose their seal, latches go awry, top lock arms get bent and worn, air seal bladders get damaged when someone foolishly opens or closes the door with the coach in gear (the 3 bladders are inflated then and subject to tearing/puncture, then afterwards won't seal against wind noise), and switch contacts get knocked for a loop.
Resist the temptation to drive with the step unrepaired and extended; been there, done that with the Pace Arrow. It wasn't pretty when I barely snagged a large rock while micro-maneuvering. You wouldn't want to have to try and straighten bent steps and even more bent linkage arms like I did, especially if they're now as clean and lubed as you indicate they are.
Joel