I have been studying organic chemistry for years, and I do not remember the spotting double bond represented with crossed lines, except maybe one ore two more times in addition to the following one
I guess it is a drawing or rendering mistake, or a representation of unspecific E/Z configuration. If the latter is true, where can I find more info on usage of this symbol?
A comment by gilleain leads to GRAPHICAL REPRESENTATION OF STEREOCHEMICAL CONFIGURATION (IUPAC Recommendations 2006). Relevant paragraph is:
The most common convention for depicting double bonds with unspecified configuration in molecules of all sizes uses a wavy bond.
A crossed double bond has sometimes been used to indicate unspecified double bond configuration or a mixture of configurations. This type of bond is not considered acceptable for general use, although it may still be required by some computer software.
There's still missing piece of information about which software and by what means it "requires" this representation.