Yes, you can measure a low RQ and still not lose weight. In a healthy weight loss process, we are aiming to get our body to utilize the fat storage as the main source of energy (low RQ) as a result of negative energy balance (caloric deficit). In a balanced diet, a low RQ means your body is burning fat as a result of a negative energy balance (caloric deficit) which will lead to weight loss.
That is not the case in a ketogenic diet, which relies mainly on fat consumption. A low RQ will indicate your body is using fat but it does not necessarily indicate that you are in a negative energy balance (caloric deficit).