I bet this was a violation of contract on Tether's part. That's far more likely than Swan lying about the whole thing.
“Throughout our relationship with Swan, Tether has consistently acted in good faith, supported mutual business objectives, and adhered to all relevant agreements,” Tether claimed.
“Conversely, Swan has acted recklessly and their actions have resulted in significant breaches by them of the agreements between us. Consequently, we have been compelled to take necessary measures to protect our investment.”
https://blockspace.media/insight/tether-sues-swan-bitcoin-in-ongoing-bitcoin-mining-dispute/
Discussion
Then again why the hell did Swan do business with Tether to begin with?