The “flowroot” is the box around flowed text. That is to say, when you type text into a box, that box has a representation in your SVG file that is the “flowroot.”
The most likely case is that you’ve still got some text in your document there that’s in a box. That could be, for example, an extra empty (or nearly empty) text box that’s invisible in your document somewhere.
You should be able to clean up the document by selecting Edit > Select all in all layers and then Path > Object to path.
If that does not immediately fix it, your flowtext may be currently grouped with something else; you may need to ungroup the objects before converting to path.
Please let me know how it goes.
(If you’re interested, you can also open the XML editor (Edit > XML Editor) to browse through the document and find the svg:flowtext element, to see what it’s attached to.)