Freezing can occur when sending USDT from the TSender contract, even if the recipient address is valid and the transfer amount adheres to allowance and balance limitations. Here's a breakdown of the scenario:

USDT Freezing Mechanism:

Tether Limited, the issuer of USDT, maintains control over the token and has the authority to freeze or blacklist specific addresses or entire accounts.
This freezing mechanism allows Tether Limited to restrict transactions involving addresses associated with suspicious activity or security breaches.
Impact on TSender Contract:

If the TSender contract attempts to transfer USDT to a recipient address that has been frozen by Tether Limited, the transaction will likely revert.
The transfer call from the TSender contract to the recipient address will fail due to the freeze imposed by the USDT issuer.
Difficulties in Predicting:

Unfortunately, there's no built-in mechanism within the ERC-20 standard or the USDT token itself to explicitly check if an address is frozen or blacklisted.
The TSender contract, relying solely on standard ERC-20 interactions, cannot definitively determine if a recipient address is frozen before attempting the transfer.