Tested the ipp with ipp://host/queue?waitjob=false&waitprinter=false for both primary and secondary printer in the class.

Same result, printjobs go randomly to the printers

new test:
socket://host/port/?waiteof=false on both primary and secondary printer-

Same result.

I found this from 2007 by delevoper M. Sweet

https://github.com/apple/cups/issues/493

Here the statement is that this issue of printing to a class where one printer is assagned higher priority to another was not implemented at that time. Ferrari: Are we really sure that first printer defined in a class automatically have higher priority than the second one in version 2.1.4?

I can't answer that definitively. It used to be that way. Things may have changed...
http://www.thegeekstuff.com/2015/01/lpadmin-examples
http://www.techrepublic.com/blog/fiv...-print-server/

In a busy network perhaps it is the first printer that responds as being available.

A discussion with Michael Sweet along similar lines...
https://lists.linuxfoundation.org/pi...14/002976.html

You might consider direct dialogue with the CUPS developers perhaps.

Yes, seems I have to do that.

Thank you very much anyway.

I'll be interested to follow your progress with developer discussions, so please report back when you have something to share.