We had a similar problem some months ago with our 401n printers connected via USB.
The issue turned out to be a firmware bug in the printer linked to the "smart install" software.
There is an option in the printer's control panel to disable this "feature".
Once disabled, the printers no longer dropped themselves offline and began working properly.
Not sure if this is related to your issues, but thought I'd offer it as a possible action.
Good luck.