My IDEX build has been working reasonably well but I have recently had a string of failures when attempting long prints. In each case, the failures occurred after several hours and always because of sticking and lost steps on the Y-axis. Sliding the extruders along the X-axis was nice and smooth, but moving the whole carriage in the Y direction was noticeably more jerky and sticky. I suspected that this was likely to be the cause of the print failures. I removed the top cover and inspected the movement more closely. The cause was then quite obvious - I had failed to keep the Y-axis drive pulley is away from the side wall and the friction of rapid to and fro movement had started wearing a hole in it. Sliding the pulley a couple of millimetres to the left has completely resolved the stickiness and binding and hopefully put an end to the failed prints.