In previous versions of Inkscape, I had defined a custom palette, and this would be the default palette each time I opened Inkscape.

In Inkscape 1.0 (on Windows 10) I need to manually select this palette each time I open the program.

Is it still possible to select a default palette?  How can I do this?

Works as expected here, in Win 8 and Linux.

Are there other elements that revert, such as snap tools or the buttons in the control bar to scale the stroke/patterns/gradients?

Could be a WIn10 permissions issue... where does the Preferences>System>User Preferences location point to?

I've not noticed any other elements reverting; palette display width options are 'sticky', for example.

User preferences points to C:\Users\MYUSERNAME\AppData\Roaming\inkscape\preferences.xml, so no obvious reason that Inkscape should lack permissions there.  Only "Inkscape data" and "Inkscape extensions" have paths starting "C:\Program Files\Inkscape".

The first thing I would try is to rename that preferences file to preferences_old.xml. Inkscape will create a new default preferences.xml.
Then I'd see if the issue persists.

I fixed the problem by moving the palette file to the path stated in Preferences>System>User Palettes.

Thanks for pointing me in that direction!