I tried CRX/BTC arbitrage into the past and it was pretty unsuccessful as I purchased on yobit and then I saw that the wallet was under maintainance and the withdrawals were not being processed, so I had to contact yobit for support and they said that the maintaiance will take a long time so I had to sell my coins at 10 to 20% loss to get my bitcoins out of there.
I noticed similar situation with EMC2/BTC at Bittrex and Poloniex yesterday. The gap looked too good to be true, so I hard to first confirm why Poloniex end was very high only to discover the coin have been temporarily disabled. Other opportunities I came across happened in the passing as such use of a bot becomes highly essential to be able to catch any opportunity.