I have a pretty capable computer, able to run M&B on full settings, and also get this issue, along with teleporting horses and no running animations. To me it happens only at night or when there are very few players though (EU servers). I read somewhere that it's just how Warband multiplayer works, it tries to save up internet usage by "predicting" what's going to happen, and the problem occurs when the client and server desynchronises. Could also be cRPG's server provider trying to save up money by limiting connection when not many people are connected and/or at night.
