Just finished building and testing my RRP Mendel. On my first print, the y-axis skipped some steps towards the end of the print. At first I thought it was an underpowered stepper or the fact that the belt traveled to one side during the print. I increased the power to the stepper by about 10% and repositioned the bearing the belt rested on to stop belt travel. It made no difference. The y-axis skipped in the exact same spot on my second attempt.

What else could cause this? Top-down and side pictures are attached.

I did notice that the corners were warping up as the bridging progressed. Could this be causing the head to catch as it travels from one side of the print to another? Is there some other, more likely cause?