I cannot be a Custom Size by the theme, since a width and height are passed.
If it is a Custom Size by the theme, the Size attribute will say as example "full", or "thumbnail" or "any_custom_name"
This ShortCode calls images in a custom size, on the fly.
See the difference in this example:
[wpv-post-featured-image size="twentyseventeen-featured-image"]
[wpv-post-featured-image size="custom" width="333" height="222"]
"twentyseventeen-featured-image" is a Custom Image size registered by the theme, while size="custom" width="333" height="222" is a custom size.
You use the "custom" one, and that does not work with the attr.
Attr, as explained, only works with "full".
==> When you clikc on filter in the black bar above, the images are displayed well as before
==> Also, I have a cloned version of this website wich is working well (same credentials for accessing admin area) !
This may be, and still the ShortCode is not to be used like that, as the Documentation explains.
It needs to be used like the Documentation explains, to be properly working
If then the issue still persists, it would be a problem in Toolset.
Right now, it seems the ShortCode is not used as it is intended to.
The ShortCodes if used like that, since not intended to be used as this, should be adjusted.