That's interesting i think Pocketbook have some series with issues with the frontlight/smartlight unregular lighting with (white spot light) and sadly i think pocketbook is aware about this issue and that is a shame.... if that true.
they said that its normal due to the e-ink technology, but that not true if all other e-ink devices in other brands dont have this issue.
https://www.pocketbook-int.com/us/warranty