i would guess it might try and write a card, then check if it was written? (i know that this is used to detect duplicated cards, which are often still writable, and flippers card emulation does not allow writes). It could be that the reader tries to write the card and expects it to be writable? idk tho, i don’t even know if you can
write mifare classic.
Potentially, the card is misidentified by flipper? Idk how likely that is, or if its even possible?
If you have an android phone you can use an app called nfc tools to get more info about the card.
All the information in this post is just my guess, i have no idea if any of it is actually relevant or not.