It's make sense why they're block your account since they have a rule to ask your identity, although the information that they ask is really far than it does. This is the reason why anyone shouldn't use centralized exchanges if they're can't send any KYC that the exchanges demanded.
I wouldn't call this is a legit scam accusations, but it's more like a warning for anyone before using this exchanges.
Perhaps the origin of your funds somewhat had a connection with Russian citizens.
4.2
You must comply with anti-money laundering obligations in order to open an Uphold Account. This will require you, as part of the registration process, to provide personal details and supporting documents (including your full name, residential address and postcode, mobile number, email address, date of birth, and certain forms of identification), and other evidence and documentation we may ask you to provide, so that we may verify your identity.
4.3
We reserve the right to require you to provide us with additional information in order to verify your identity and/or require you to undergo a background check prior to being authorised to use Uphold’s or its affiliates services, or at any point thereafter, in accordance with applicable laws and regulations. You acknowledge and agree that we may make any inquiries that we consider necessary, either directly or through third parties, concerning your identity and creditworthiness including, without limitation, requiring you to take steps to confirm ownership of your email address or financial instruments, ordering a credit report, or verifying information against third party databases or through other sources. These inquiries and verification may involve the sharing of certain aspects of your information with third parties for the limited purpose of completing these inquiries and verification.