Why do axis lines disappear when opened outside of Inkscape?

Question

I made an svg graph using R (ggplot2) and it displays fine in Firefox.

I then edited it in Inkscape to improve the legend. In order to do this, I had to ungroup a group that contained both the legend and the axis lines. This is what the graph looks like in Inkscape (data removed for confidentiality)

However, when I save the file and open it with Firefox, Edge or Word, the axis lines and the axis ticks are not displayed:

If I open the file again in Inkscape, the axes and axis ticks are still there.

If it helps, the axes and the axis ticks are polylines. I've tried regrouping them before saving the svg, but that didn't help.

What could it be and how do I fix it?

Answer 1

My guess: There's something that Inkscape reads right but writes wrong. To clear the problem convert the problematic elements to paths. Use Path -> Object to path and Path -> Stroke to path. Try at first Object to path.

Check the structure in the Objects panel to access the parts which need conversion. There can be a mess of nested groups which look impenetrable if it's made in another program. The same happens often when one imports PDF files. Inkscape has a brute force extension Arrange -> Deep Ungroup to clear the jungle if needed.