In MUX when adding a total row and per-period metrics is greater than 100 periods, the totals show 0.
Clarity all versions through 16.3.3. Future versions may be updated.
This is working as current design.
There is a cutoff of 100 per-period metrics where any totals calculations will not work if more than 100 periods.
Work around is to change the per-period metrics to a different period value (quarters instead of month) or make the Start and End Period dates for the options result in 100 per-period metrics or less.