The program once in a while tries to refresh fetching what the current rewards are for the various pools.
Some of the parsers are currently broken, i.e. Eligius (it tries to look them up for /us/ and /eu/).
Every time an error happens there, the thread dies.

You can find out what caused by scrolling back in the log and seeing what error messages there were between when it was last online, and the first time off-line.
Effin' threads.