Alexim: In the general catalog view of GOG you can only see up to 10k products at once due to limits imposed to improve performance. This is creating a series of false positives on GOGDB, which considers more and more games delisted, all those exceeding the ten-thousandth game after being sorted alphabetically.
The same problem has occurred before, when GOG reached 1,000 and 2,000 entries, but they resolved it back then pretty quickly (within weeks, IIRC).
MaGog handled this issue, while it existed, by retrieving the catalogue in two separate queries, based on release date. The same could theoretically be done here, for example getting first all games up to 2020, then all those from 2021 onward. But back then every single game had a release date, whereas now some are missing it.
Perhaps querying by price range (e.g. 0-4.99 and 5.00+) --- which didn't exist in the MaGog years --- could be used instead. This would need to be supplemented by querying for upcoming games, many of which do not have a price.