The current status is the following:
With the current cap of 100 players per server, the load is now at near 0% (the lower the better, 100% means the CPU is completely locked up).
This is really great as it appears that the servers can, as planned, handle a lot of players.
The bad news is that whenever a new player logs in, it adds a bit of CPU overhead, which means that the CPU must work extra hard for a while (it collects information about the character from the database clusters and instantiates the character on the server).
This was not noticed during the Alpha Test, because we did not have hundreds of players trying to login at the same time. It was also not noticed during our performance tests because in those cases we had thousands of "player bots" already created on the server when we logged in.

So, basically what happened was that each time we restarted the server and told everyone it was back up, hundreds of people tried to login at the very same second, causing the CPU to lock up more and more, until eventually the server froze.

What we're working on to fix this is to implement a queue system. This system will mean that players will be in a queue before they are logged on, which means that the CPU overhead caused by the loading process will not cause issues.

This is not a five minute task, it will take some hours to complete this, but we hope it will solve the situation and therefore be worth the extra wait time.