This is another issue that I know several people are facing (across different servers). For some reason, Thralls have great difficulty going up or down stairs. As expected, the problem increases in frequency and duration as server latency rises. However, it can also occur even with low latency.
In some cases, they switch to the running animation but remain stuck in place, requiring you to move far away from the NPC for it to teleport. It may just be an impression, but Wild NPCs apparently show a lower tendency to this problem.
As always, if this error has already been cataloged or is not considered relevant to address, please disregard it.
