I lost some cards from a list recently. From what I ended up seeing, some were evidently from sets that were previously present, deleted, and reposted, likely because they were under the wrong name, or classified incorrect as inserts or something like that. Sadly I do not remember the sets in specific, but the handful of cards that I lost were baseball ones from the early to mid 2000's. For example, I know this Jason Simontacchi card -
https://www.tcdb.com/ViewCard.cfm/sid/277888/cid/16943084/2002-Donruss-The-Rookies---2002-Donruss-Best-of-Fan-Club-Update-218-Jason-Simontacchi
- was one of the cards that I lost and eventually re-added to the list. The card's image was wiped, and the player's name was gone from the card description in the list, but the card number and set name remained. I believe this set was re-classified as an insert, hence the issue. Either way, I'm not sure who did this, but it seems like it was fairly disruptive. Not sure the full extent of cards lost, but I know I lost cards of a handful of players. Most seemed to be from rookie insert sets, and 4 of the 6 were from 2002 sets. Sorry I couldn't be of more help, but this might be your issue, and hopefully someone knows more about what exact changes were made to help you rectify them.