In the last 3 months or so the credit card companies are being much more fierce with declining credit cards. I have seen a massive increase in the number of declines.
When people have their card declined they often try again 3-4 times (especially if they know their card is good), which would cause higher traffic and load for their servers.
In the next few weeks I am going to put up a big sign for people who have their cards declined telling them to call their bank and not keep trying. There is nothing I can do as a retailer, its probably the same for moniker.