Fix custom visuals no longer working with no internet connection

We run PBI Report Server in an environment that does not have an internet connection. All the custom visuals stopped working with some update this past year: we cannot add them to reports - the status says they are added successfully but they *never* show up in the selection panel, just a never-ending spinning circle.

On existing reports that were built before the change, the visuals *normally* continue to function but break if any changes are made. Other, random, unexpected behaviours happen and our only option is to remove them and try to "make-do" with standard/default visuals.

Would it be possible to have custom visuals work once again without internet connectivity?

Thanks