*update:
My hypothesis does not seem very valid. The trading volume and intra-day prices for 1ST on OKEX are below the Bittrex's for both BTC and ETH pairs.
I still can't understand the reason 1ST was under maintenance on Bittrex for 2-3 days. It's an ERC20 token and does not require wallet upgrades/blockchain sync, as independent coins do.
My first hypothesis would be;
If the wallet has been in under maintenance for 3 straight days, that means no new coin can come in and traders have to trade with that very limited supply.
Second;
Delisting might be coming. It's known that after bittrex announces delisting of a coin, it gets pumped for one last time. Of course there is no such a thing that 1ST will be delisted but if someone got the news before anyone else, this pump might be a goodbye to 1ST.
Third;
If you look at closely to Bittrex chart, you will see the flash crash. Someone dumped from 5K sat to 111 sat. That's a crash. Someone might have picked up coins from dead cheap prices, pump it more to get more Bitcoin.
Another perspective would be one desperate 1ST holder, saw that wallet in maintenance mode for 3 days and decided to dump it.
I would go with the third option.