I am not sure how to ask this, but I will try my best.
I have replaced some missing values in a feature with the mean of the feature conditional on a second categorical feature. However, not all missing values were replaced because some categories of the second feature did not have any values in the first feature, so its mean cannot be calculated. Then, I tried again by replacing the leftover missing values with mean conditional on a third feature. The third feature also contains values that were just replaced with the mean of the first feature. So, is it alright to replace missing values with the mean calculated from values that include some that have once replaced other missing values?