Cleaning and relubing the chain can't be the culprit all on it's own so something else happened when you did it. Try turning the crank backwards slowly and watch the chain as it comes off the lower rear derailleur pulley to see if there is a tight link or a twisted or damaged side plate.

BTW, did you remove the chain to clean it and, if so, did you use the required special reinstallation pin? Did you install the pin properly?