Somebody keeps on trying to send around $1m USD through Tether but the txs keep on getting not included with a message saying "Reason: Sender is frozen for the property". Can Omni freeze anybody's USDT when they want to? And if so, what was this offender's problem? A hack?

Example: https://omniexplorer.info/tx/8adb714f1e65e1cb0fdfe8d9003caacd04586c01fb238db49819822aac7ed97b and https://omniexplorer.info/tx/024d461cd7e8514ebcb0356ddc14aaf4efaedb6c5334614e72ef255259ae1889

well
probably they,i mean the 2 address u say have a illegal transaction , or something like that.
just my opinion.
because if u see this
https://omniexplorer.info/tx/acf600d636454e364e709d7d01d02c60092b127e663be66153bf981ab898ee5a
the transaction is valid.