KYC is required if the user has reached the withdrawal threshold and shuffle.com does not explain what the threshold amount...

If Shuffle use these for their platform and KYC requirements on their users, they have to write it clearly in their ToS. They can not arbitrarily pull KYC card anytime they want and it is only harmful for their reputation.

4. Know-your-customer (“KYC”)

4.1. We reserve the right, at any time, to ask you for KYC documentation if we deem it necessary in order to determine your identity, location or age, or for any other purpose. We reserve the right to restrict your ability to access any or all Services or to make payments or withdrawals until your identity has been determined to our satisfaction, at our sole discretion.

4.2. We reserve the right to disclose your information to third parties as appropriate to comply with any legal process or as otherwise permitted under our privacy policy, and by using any Service, you acknowledge and consent to the possibility of such disclosure. Please refer to Shuffle's AML Policy for more information.