Sub 50g of carbs works for some people. One thing you have to be aware is different people have different carb thresholds to maintain ketosis. If you are stagnating in weight loss it might not be lack of ketosis but as mentioned by others your body adapting and adjusting to change in metabolism and hormones. Sometimes adding resistance training will give you the metabolism adjustment needed to get rid of last stubborn fat with adjustment to protein and carb. You are not trying to it new maximum reps so don't worry if you feel weaker at first. The idea is to burn hard glycogen stores and give your body added metabolic burning while maintaining ketosis. Everybody has a different metabolic reaction to restricted calories/ketosis so you have to find the sweet spot.