The Ethereum Layer 2 network, ZKsync, has issued a notice on platform X that during the protocol upgrade v26, backward compatibility of the Mailbox contract temporarily encountered issues which may affect L1→L2 transactions. This is because these transactions were initially handled by the Mailbox contract. However, due to different transition stages between bridging and L2 during the v26 upgrade period, backward compatibility temporarily does not work.
It might take about 1.5-2 weeks to resolve this issue. Therefore it's recommended for users to use "requestL2TransactionDirect requestL2TransactionTwoBridges" on BridgeHub instead of Mailbox and also suggested migrating to BridgeHub in order to avoid future deprecation of the Mailbox contract.