If you are using multiple years in your report, this may bring multivalue error. You can try adding [Year] and [Time] also to the end of the formula:
=NoFilter(RunningAverage([TagMeasure];([v_Month]))) foreach([Day]) in ([Year];[Month];[Time];[TagName])
I wrote at my first answer [TagMeasure] instead of [TagName] by mistake at the end of the formula. You should change it ofc.
Hope this one helps.