[Jamming] ProC900s - Constant A3, A4 sef Jams at paper exit (simplex only)

[sav1973]

Hi All

Am having a problem with a Proc900s.

I'm getting constant jams at the paper exit (7504-090)

It's only occuring when copying/printing A3 or A4 sef simplex, duplexed will feed through fine. I've removed the streampunch/finisher so I know that's not the issue.
It feeds about an inch out of the machine and then just stops. Have tried with 80 gsm and card, same.

Any suggestions would be much appreciated.