Are you sure you correlate this issue with partition resize? You sure that was only system change between smooth auths and slow ones
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Don’t take it personally I am often guessing the wrong cultprit because I have biases from previous successful update.
Could it be that you had Stable update? There is a change to “pam” auths and they maybe timeouting on some module maybe?.
Maybe that could be cultprit.
P.S: - I am also only guessing