SVG export is broken in Illustrator 2018 - how can I use the old version?

I'm editing SVG files with Illustrator that contain objects with various properties, for example:

• Paths with 50% opacity
• Circles
• Invisible objects

The SVG files are processed automatically in a later step outside of Illustrator. In this process, the properties above need to be preserved exactly as they are. Until now, I could use the Illustrator export function. With Illustrator 2018, the export function doesn't work properly anymore: No matter how I do the export, either using the "Save as..." option, the "Export as..." option or with custom JavaScripts, something is broken. Sometimes, circles are converted to paths. Sometimes the objects with 50% opacity are rasterized. Sometimes the invisible objects are not contained in the exported SVG. Sometimes there is an error message "Transforms are expanded".

After reading in the Illustrator Help, the Illustrator JavaScript Guide, and browsing the Forums, I still don't understand how to precisely control these export options. I also don't understand at all why this is broken - my scripts worked fine with earlier versions of Illustrator, but now the exportFile() method and the ExportOptionsSVG object appear to work differently?

I have now installed earlier versions of Illustrator: 2015.3 and 2017. I have sucessfully edited and exported SVG files with these versions previously. However, now these versions show the same bugs, it looks like even when I run the old versions of Illustrator, the new, broken SVG-exporter is used.

I really need this to work again. How can I use the old Illustrator SVG export? Or, alternatively, how can I precisely control the export options so that the SVG export works as before?