Mmm. If their systems were overstretched last week by a heavy volume of trading, it wouldn't be astonishing if they are also overstretched this week when there is another heavy volume of trading.
They offer a very modestly-priced brokerage service, and I guess part of the business model must involve keeping their own costs to a minimum. Customer support is supposed to be poor — I have no experience of it myself, but I have heard this said — and it wouldn't amaze me if their IT systems didn't have the same amount of spare capacity, backup options, etc as some others. Hence they might be more prone to not performing well at times when they are stretched, like now.