If you're not there then there's no way to know the trigger.
For now for the safety of the dogs separate them completely while you're gone, either in crates or separate rooms while you're gone. Find a good trainer to do an evaluation in person and find out what they need and how to implement it
I hope both animals recover quickly and you’re able to prevent further fights
Jasmine - Female Miniature Poodle - born Aug 15, 2010
Loker Delgado Von Stalworth - Male GSD - born Jan 26, 2012
Koda & Zazu - 5 year old male cats
Alex - Male Cocker Spaniel (rescue) - RIP Cuddlebug 2007-2010