Hey There, I'm Alpha Jenner. There could be a number of reasons responsible for your printer saying offline during the print job. Here’s the list of Why Does My HP Printer Keep Going Offline. The following are some of the most frequently cited explanations: There is a problem with the connection between the computer and the printer.
https://www.hpprintersupportpro.com/blog/stop-my-hp-printer-from-going-offline/