OS: Debian 9
Inkscape version: 0.92.1 r15371 (Sorry cannot upgrade due to Debian's stability policies)

When I start a new document, the measurements on the ruler are always in pixel. If I click the drop down menu on the document preference to change the measurement unit to inch or any other unit, nothing happens. If I open a new document from a template, changing the measurement unit works instantly.

So I suspect there is something maybe in my default.svg that is conflicting with the current version of the software since it was build on an older inkscape.

Now I tried to delete all default.svg from my system. Inkscape starts on a "Memory Document" which also have the same issue of not responding on measurement changes in the document preference.

I also tried the generic canvas and a few other template they all seem not to have that issue.

Not sure if this issue is solved in 0.92.4
Not sure if there is a way to convert my old default.svg template to retain the measurement unit.

Right now I am thinking in creating a new default.svg from a template as a temporary solution.

The temporary solution seems to work. After a lot of struggling, I managed to create a new template and it retained inches as measutement.

I don't know if we could troubleshoot the old default.svg. But if you'd like someone to try, please share that SVG file.

Meanwhile, hopefully your temporary solution will keep working.