Referenced files in FM2020 missing

Hello

I have framemaker files in which image files are embedded by reference via web link.
So the reference path has the following form: https://www.xyz.de/xxx/yyy/...
The image files are in png or eps format.
With FM2019 (structured), this type of reference was not a problem.
However, after switching to FM2020, the image files are no longer found under the same conditions (same files, same computer, same operating system, same access rights, etc.).
Does anyone have an idea what could be the cause?

Thanks

Stefan