System uptime isn’t written when Kodi exits anymore. This is intentional and related to an issue that was quite annoying last year: Skin changes lost after a reboot.
I’ve made some changes to how and when settings are written to guisettings.xml in Kodi. As a consequence, we don’t bother writing the uptime when Kodi is exiting. See
If we revert this patch; then uptime will be saved, but there is a great potential for settings to be lost (skin change is most common symptom) when rebooting; particularly if Kodi hangs due to a bad / poorly written add-on.
Sam