It was recommended to us that these would fall under a Reg E Investigation and that we could hold the funds for 10 days while we investigated.
There's no such thing as "provisional debit" in Regulation E. Since these deposits don't involve checks, Reg CC holds also do not apply.
What you likely have here is a money mule sitatuion where fraudsters have used stolen card information to either issue fraudulent refunds for purchases that were never made or fraudulent P2P transfers through Venmo, PayPal, CashApp, etc.
As Randy states, the first step is to contact the customer to inquire about the source of these credits. You should review your account agreement as any ability to hold funds during a fraud investigation would be stated there.
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