The grounds for this are specified in the "Payment Terms":
Item 3: "The Company may delay for a necessary term, but in no case more than 90 days ("Investigation Period"), and/or cancel any collection of Donations from the User and/or the following payment to the Broadcaster for purposes of preventing unlawful activity or fraud, risk assessment, security, or investigation."
It often takes some time to conduct an investigation, and each case of a blocked payment is examined individually. For the entire duration of the investigation, the funds remain in your account balance and continue to belong to you.
Funds can only be deducted from your account in one case only: if the bank informs us that a payment has been revoked. This confirms the fraudulent nature of the transaction, and the amount of the payment is instantly and fully refunded to the payer.