This is a theory, but I've noticed that sometimes one or more skills will bug out - a weapon skill will start performing extremely well or extremely bad for a stretch of time, or an ultimate will stop working or disappear. Sometimes I will be unable to use any skills at all while an enemy wails on me.
Sometimes I cannot kill a specific enemy, and it feels like all my skills are 1/10th of their strength. I log out and log back in, and just clobber the same mob, having done nothing differently. I've seen other things too, like spell effects remaining stuck to characters, like a blue cloud around their feet, and similar things. This looks to me like processes not completing and cleaning themselves up.
One thing I have noticed that fixes issues that don't go away is to respec. In my case, my 'Q' potion slot stopped working entirely, and my ultimate would never regenerate anymore. After my respec, everything worked right again.
If I were to connect the dots, I might suspect that some of the calculations or even the status of attack powers are losing communication between the client PC and the megaserver. If that were true, could some skills or even skill lines get borked, for short or long durations of time?
I know this all sounds vague, but I don't know how they coded this. Basically what I'm getting at is - if there is any kind of cache on the server side for a character's skills, if that gets corrupted, it might stay that way.
Can anyone more familiar with how server/client works comment on this?