This is a very old bug (www.wizard101.com/forum/halstons-laboratory/choppy-stuttering-skipping-8ad6a41b4937464a0149447fe4662838), but I think I know something of a cause. If your Quest Helper (the yellow arrow) is set to On, but there are no quests available, it will freeze every second as it tries to update it because there is no yellow arrow to display. If you turn off the Quest Helper or go into a place where there is no arrow, like your house, the freezing stops. There are also large dungeons where a quest will show up for that location and display the arrow (i.e. Tartarus, Xibalba). During that time, there won't be any freezing, but the moment the dungeon is completed and that arrow goes away, the freezing returns until you turn off Quest Helper again.
I discovered that if you turned Quest Finder off rather than Quest Helper, this will also eliminate the stuttering problem. Apparently, this started when Quest Finder was added, so maybe this will help them track down the issue.