Import fails because of unable to open image

Does someone as experiences with this error message when importing a site?

./flow site:import --package-key="My.Package"

During the import of the "Sites.xml" from the package "My.Package" an exception occurred: Error: During import an exception occurred: "Could not convert target type "Neos\Media\Domain\Model\ImageVariant": Unable to open image /home/user/Neos/Data/Temporary/Development/ResourceFiles/8b8e7bbeb082294705ede1f94285d86c7904c2c2-1548288567.6834-565"., see log for further information.

I appreciate your help.