Hm maybe this doesn't count but when I still played runes of magic there was this daily guildwar with rediculously good rewards. Even if you lost. Problem is the servers couldn't handle the traffic resulting in freezes, crashes, random disconnects and so on. It was so bad that it was more of a logging-back-in war than an actual guildwar. Often you'd pretty much just be going from desktop to login to character select to crash and back to desktop for an hour.
Also, another ftp mmo I once played had this problem that if you tried to log into a full server your computer would crash forcing you to reboot completely. And the servers were ALWAYS full. SO actually getting in and playing could easily take hours during peak hours. Or you could get in on the first try if you were lucky.