I think you can start with simple things...

There is a difference for Visio between numbers and strings, e.g. between 5 and "5", although they look exactly the same. 5+5 => 10, but "5" + "5" => "" in the report.

You need to make sure that the properties you are using can be added. Just set their type to "number", that should solve empty Totals for the "Weld Length"

Second, time intervals. Visio does not provide much of the formatting for the totals field. For the time intervals, the results appear to be in days (!)

And the default number of digits after the decimal point is 2. Therefore, if you have for example 1:00 minutes (em) and 5:00 minutes (em), that would result in 6:00 minutes total,

but if you recalculate that to days, that will be 0.00416 days (ed), and if only two digits are displayed, that would be 0.00 days.

Hope that clarifies the results you get... I am not sure how can you go about intervals.

Visio Shape Reports do not seem to support formatting of the totals.

Looks like Visio could have used formatting from the property for which it calculates totals, but apparently, it does not do that.