Probably has something to do about “hardware clock” (hwclock command) on the Real Time Clock (RTC) chip vs software time (date command) - which adjusted by the OS according to current device location setting.
I don’t know which time KOReader uses, but you might try syncing those teo on Pocketbook side (it is a Linux). Although I only tried this on Onyx Boox Kon-Tikie 2 and once screwed up the clocks so my internet stopped working correctly
so here be dragons