I understand that when Around is used in computations, uncertainties are by default propagated using a first-order series approximation, assuming no correlations. On the other hand this makes it impossible to propagate uncertainties where one variable appears more than once in the formula, even if all the variables are uncorrelated to each other, because it looks like Mathematica is considering every appearance of the same variable as different variables. Take for instance:
a = Around[7,2];
4a yields 28pm8 (correct result) whereas a+a+a+a yields 28pm4 (wrong). Well, in this case it's obvious how to solve the problem, but if we need for example:
Mathematica yields 8.9pm2.0 and I haven't found a way to get the proper result 8.9pm2.3.