KYC is required if the user has reached the withdrawal threshold and shuffle.com does not explain what the threshold amount, generally when withdrawals reach $2000 to $10000 and this is normal for every casino that has a license because this is a global rule.
Exchanges and casinos can have lifetime trading, withdrawal thresholds for different KYC levels.
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.
I didn't see accusation against Shuffle so assume they are good but to avoid damage on reputation, from now they can return to discuss internally with their Compliance team, lawyers and finalize their service terms on KYC, and add it to their ToS.