Sorry about adding to an old thread, but I'm having a similar issue with my machine.
No changes to connection or wiring, no warning or error messages are displayed on the printer or in VersaWorks and all ink bags are showing 1/2 full or better. I thought maybe file size could have something to do with it, but it seems to stall after passes randomly.
Here's a video to show what I mean..
https://signs101.com/media/roland-vg-640-stalling-between-passes.9733/