I use the comand
> inkscape file.svg --verb=EditSelectAll --verb=ObjectFlowtextToText --verb=FileSave --verb=FileClose --verb=FileQuit
and if one convertion of ObjectFlowtextToText fails, Inkscape does not do anything, also there are some Flowtext that are convertable:
```svg
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd" [
<!ENTITY ns_flows "http://ns.adobe.com/Flows/1.0/">
]>
<svg viewBox="0 0 1200 5486.5" xmlns="http://www.w3.org/2000/svg" xmlns:ns1="http://ns.adobe.com/Flows/1.0/">
<flowRoot>
<flowRegion>
<rect x="54.286" y="88.571" width="202.86" height="62.857"/>
</flowRegion>
<flowPara font-size="56">Retinol</flowPara>
</flowRoot>
<flowRoot transform="translate(-39.738 -34.7)" font-family="sans-serif" font-weight="700" letter-spacing="0" word-spacing="0" style="line-height:.01%" xml:space="preserve"><flowRegion><path d="M140 25.714h991.43v108.57H140z"/></flowRegion><flowPara font-size="72" style="line-height:1.25">First-generation retinoids</flowPara></flowRoot>
</svg>
```
(The first flowtext is not convertable because the rect is too small.)
The full file can be downloaded here:
https://commons.wikimedia.org/wiki/File:Retinoids2DACS.svg
(see file history)
confirmed on Windows 10, Inkscape 0.92.2 (5c3e80d, 2017-08-06)
- load the file MinimalWorkingE
- perform Edit->SelectAll, get 10 objects
- perform Text->Convert To Text
- get status message at the bottom saying "The flowed texts must be visible in order to be converted", and no conversion occurs.
- delete object with ID = flowroot16
- now repeat the conversion operation on 9 objects and it works