This has been happening to me during World Boss fights constantly for the past few days. I never had any sort of issue like this until this week, there’s been no recent hardware/network changes, and I have no issues whatsoever in any other programs. I’m in central NJ with Fios (50/50mbit plan).
This makes it pretty much impossible to do some bosses for the dailies, since so many people show up and some of the fights (especially Jormag, today’s) take so long that I’m bound to get hit by the issue before the fight ends.