Sorry I'm not following you - the job sheets and the coloured separator sheets have identical media attributes.
Are you setting the weight in the driver or just leaving it as Use Machine Settings?
I've noticed Fiery will cause a machine to cycle between tray calls if the weight is not set in the driver.
I run an iGen 5 - 150 with Fiery RIP.
I'm running 300 sets of SRA3 single sided.
Each set comprises 190 sheets and 1 sheet coloured separator.
At the end of each set the machine cycles down and waits for approximately 30 seconds before cycling up and carrying on.
The media attributes are identical for the job sheet and the coloured sheet so I guess it's not fuser temperature.
There is no message in the Active Status List.
Any suggestions would appreciated.