Every USDT transfer ever made is on a public record, and there are companies whose whole business is reading it. They follow money from address to address and give each address a score. Money that passed through a hack, a scam or a sanctioned service carries a mark, and an address that receives it picks up some of the mark too.
Here is the uncomfortable part. Nobody can refuse a transfer. If someone sends USDT to your address, it arrives. There is no "return to sender, unopened". So when a stranger, a customer, or a customer's customer pays you from an address that is already flagged, your address has now touched flagged money, and the people scoring addresses do not stop to ask whether you knew.
Imagine being handed a banknote that was in a robbery last year. With cash, nobody would ever know. With USDT, the serial number is public, the whole history of that note is public, and there is an industry whose job is to read it. You did nothing wrong. Your address is flagged anyway.
Tether freezing your address is real, and rare. The version that happens to ordinary people all the time is the exchange: it watches the same scores, and it freezes your account first and asks questions later. The habit that keeps you clear of both is on one page:
FROM HYGIENERead the long version