IC Markets freezing up

Well, should it? A stop loss is a market order. In a fast moving market, that is, on news releases, weekend gaps etc., negative slippage on market orders is kind of normal. Unless the broker does it artificially.

What is really bad about ICM is that they execute limit orders as market orders.
Normally, if you want to protect yourself from negative slippage, you can use limit orders to enter a trade and take-profit orders to exit a trade. This way only positive or zero slippage is possible. But it just doesn't work here. ICM treats all orders as market orders so you can still get negative slippage. Terrible execution.

With every forex broker your orders are "market orders",cause you pay the spread. Proper limit orders will work with futures only, there you pay commission but they execute exactly what you want.