"To release the deposit" means to return or give back the money that was put aside as a security or guarantee, usually in a financial transaction or rental agreement. Full definition
My understanding is that the seller's consent to release those deposits back to the buyer when a condition is not satisfied is built into the Agreement of Purchase and Sale. (remonline.com)
They are switching banks to one that can safely handle their high volume of transactions, but the current one hasn't released the deposited funds for some reason. (biggerpockets.com)
For certainty, the authority to release a deposit from a brokerage trust account should be established by a separate written agreement signed by both parties. (recbc.ca)