I think you are correct; the decline from May to today is probably due to the surge in the Canadian dollar.
If you look at this chart, May is about when CAD started to trend upwards:
I don't hold VFV.TO, because I use the regular portfolios, but I know my overall portfolio value (when denominated in CAD) has fallen a bit as the Canadian dollar has strengthened.
I try to either not pay much attention to it, or to look on the positive side: now it's cheaper for me to buy more USD; or, in your case, cheaper to buy more VFV.TO!
Hope this helps.