Ive been chugging away at some prints on my R1+ running Marlin 1.1.7 with UBL. PID Tuned/Z Offset and the obligatory G29 P1, G29 P3 T, G29 F10.0, G29 S1, G29 A, M500 to probe the bed and create a saved mesh. Multiple prints without so much as a panic from the printer. Just adjusting settings back and forth trying to improve the print quality. After printing out a batch of prints on the bed, I had to adjust where on the bed it was going to print in Simplify 3D to avoid a chip in the glass bed. I changed to a different design from the same package, set the prints offset to the right, without a print in the area of the chip. Told it to start printing and shortly into making the skirt outlines the printers z-axis went straight to the top and started banging the case. I went back through, fixed everything, recalibrated and tried again. This time with my mouse ready to click emergency stop. Same point in the outline, z axis started going straight up vertical again. I then tried an alternative design from the same package for the item I was trying to print. Placed them in the same locations, started to outline on the bed and then the z-axis went plunging into the bed. This pulled the z stop and carrier off the nut. Its currently apart and ive fixed that. Could these two print files be purposely causing the z axis to go straight up and straight down? Its repeatable. Or does this have something to do that its printing up close to the heated build plate line on the bed? I noticed that the left side of the machine has a stop triggered by a screw when the carriage goes far left, but the right side of the machine has no stop. Simply allows the bracket that carries the extruder to strike the plastic clip that stops the z axis carriage from riding off the switch too far.