Glo Glo stalls during scan of reloaded collection ?.

Kobo Glo v3.12. All epubs sideloaded.

I deleted all books in my Glo using the remove function in settings.
I transferred my entire collection from Calibre to Glo, transfer Ok.
I disconnected from PC and the Glo's scan feature started, but it stalled at 80%, I left it for two days and the progress bar didn't move past 80%, pin hole reset was required to restart the Glo, Zero books in it.

I connected Glo to Calibre, Calibre shows that books are in Glo.
I re-deleted all books via settings and proceeded to transfer books from Calibre to Glo piecemeal, after each small transfer I disconnected the Glo letting it scan, then I'd reconnect the Glo to Calibre for another transfer.
It took forever but ALL books were successfully scanned by the Glo.

1). Why would the glo hang during the scan of the entire collection and not during the piecemeal reload and rescan ?.

2). If it does encounter a problem book, why doesn't it skip that book and continue ?.

Suggestion:
If there are problem books that it stalls on, skip them and continue with the loading of subsequent books, then display a fault log at the end.