In this case, the sentence reads "You must have made your weekly claim for benefits for the week ending [date] by [date]".
This is referring to the fact that a person claimed a week of benefits too late, and should have claimed them earlier. However, while "must" is generally considered a stronger word, in this case it sounds more like we are saying "We think you claimed benefits this date, but we're not sure." Am I correct in reading it this way? Would the sentence be clearer if it said "You SHOULD have made your weekly claim for benefits for the week ending [date] by [date]"?