[Quoth]

It's why even on the Marvellous Kobo you have to connect twice:
First to send the book.
Second to update the Series data in the Kobo Database as it won't get it from the book.

Thus if you reset or logout/login on the Kobo, the books are all re-imported but the series names/data is lost. You need to either restore an up to date backup copy of the database (which will restore reading status etc too) or have Calibre update the series data. This can be done via Kobo Utilities after selecting all books with series info and Update Metadata.

I only use the Kindle for Tests now as the later ones only work sensibly for Collections and Series if it's an Amazon title with series info in Amazon library and Collection is synced/done on device. My ancient Kindle DXG old Sony work better for Collections than any more recent Kindle.
99.5% of my books are PD, so the series data is usually created by me on Calibre.