IMAGE IN POP UP DOES NOT SHOW UP [MULTISITE INSTALLATION]

Image in PopUp Pro does not show up.

On my site the image class looks like this:

<img class="\"aligncenter\"" src="\"http://nnmp.zagan.pl/wp-content/uploads/sites/4/2015/09/pp-A3-3.jpg\"" alt="\"\"" width="\"566\"" height="\"800\"">

Refreshing or changing permalinks structure does not help.
Would be nice to have a solution as soon as possible.

In the PopUps List - Preview is showing image correctly.

In Edit mode and on site - not.

It doesn't work on every site.