5.1.0 Bug - Printer Hangs when starting multi-color print  

5.1.0 Bug - Printer Hangs when starting multi-color print

This issue was independently discovered by both myself and another user who posted about it on YouTube.  We both were printing in nearly identical ways, so it might be a bug that is very particular to a specific use case.

We both were printing multi-material prints on our MK4's, but with a virtual MMU (manual color changes).  So we tell PrusaSlicer that we have multiple extruders, and use a custom Tool Change GCode to call M600.  The other guy didn't use a wipe tower, I did, seems irrelevant either way.

The files were exported as ascii gcode, not the new binary, and placed on the USB.  Then we started the print on the printer.  As soon as you start the print, it hangs on a black screen, no matter how long you wait it just stays there.  If you pull the USB stick out, the printer jumps back to the home screen, so it's not completely frozen.

We're both using PrusaSlicer 2.7.0 final and firmware 5.1.0 final.

I found a workaround, if I started the print via Prusa Link it would actually print, though Prusa Link would hang shortly after starting it, yet the print finishes okay.

The other guy changed to using binary and starting via Prusa Link, and he says that is working great for him.  I've not tried binary, and I don't think he's tried binary starting from the printer, so it's unclear if binary solves anything, but definitely using Prusa Link solves part of the issue.

Note that we've both been printing successfully with a virtual MMU for a long time, and our process hasn't changed, so it was either the upgrade to PrusaSlicer 2.7.0 or firmware 5.1.0, or the combo, that introduces the issue.

Paul