Bitfinex recently moved from Noble Bank to HSBC. This had caused a disruption in deposits, and a significant ($50+) BTC premium on USDT based exchanges.
Comparison of multiple exchanges, note how Bitfinex, Poloniex and Binance are higher in price than Bitstamp, Gemini and Coinbase.

Bitfinex released a statement, saying that nothing is actually wrong, that the deposit delay is resolved. https://medium.com/bitfinex/a-response-to-recent-online-rumours-677de7c4d171 (https://archive.fo/kZbmG)
USDTUSD pair on Kraken, showing that the price of the USDT has not recovered, despite assurances from Bitfinex.

I do not hold any USDT at the time of this posting, for obvious reasons. Bitfinex can make statements all they want, but the chart disputes their assurances.
Comparison of multiple exchanges, note how Bitfinex, Poloniex and Binance are higher in price than Bitstamp, Gemini and Coinbase.

Bitfinex released a statement, saying that nothing is actually wrong, that the deposit delay is resolved. https://medium.com/bitfinex/a-response-to-recent-online-rumours-677de7c4d171 (https://archive.fo/kZbmG)
USDTUSD pair on Kraken, showing that the price of the USDT has not recovered, despite assurances from Bitfinex.

I do not hold any USDT at the time of this posting, for obvious reasons. Bitfinex can make statements all they want, but the chart disputes their assurances.