I can see the problem, and offer a temporary solution.
The result in Gimp 2.10 is 32 bit linear FP whereas from Gimp 2.8 it is 8 bit gamma integer.
Probably the filter need updating with a switch for those precision modes.
A fix. Use the old smooth-palette.exe plugin from Gimp 2.8 It will take precedence over the existing.
You obviously still have a Gimp 2.8 For others the filter is attached.
The usual unzip and put in C:\Users\your-name\AppData\Roaming\GIMP\2.10\plug-ins
Should be reported as a bug/improvement. Fallen out with that issues site, leave it for someone else
Yep, do not hold your breath hoping for a fix. https://gitlab.gnome.org/GNOME/gimp/issues/1010
The result in Gimp 2.10 is 32 bit linear FP whereas from Gimp 2.8 it is 8 bit gamma integer.
Probably the filter need updating with a switch for those precision modes.
A fix. Use the old smooth-palette.exe plugin from Gimp 2.8 It will take precedence over the existing.
You obviously still have a Gimp 2.8 For others the filter is attached.
The usual unzip and put in C:\Users\your-name\AppData\Roaming\GIMP\2.10\plug-ins
Should be reported as a bug/improvement. Fallen out with that issues site, leave it for someone else
Yep, do not hold your breath hoping for a fix. https://gitlab.gnome.org/GNOME/gimp/issues/1010