I think you will never have problem with a crypto coin exchange if you conduct active trade. If you use it as a coin storage with occasional buy/sell, then I think chances are high that one of your transactions will get frozen or your account scammed one way or another at some point. At least this is what I observe. I have yet to read any complain about any exchange from someone who trades actively and not just moves coins around.
Exchanges make moneys out of your transactions, the more transactions you have the more valuable your are for the exchange. I won't be surprised if the exchanges have presorted groups of users, with different attitude towards them based on their activity. With ones being more prone to be scammed that others. Why scamming someone who pays you regularly? Not profitable, if you ask me...
The exception is when the coin fucks up, which is unrelated on how you trade.