Hello,
The clock for ARRIA 10GX SI Development Board is meant 125MHz. So what you're observing while feeding 156MHz is expected.
Kindly refer to Installer Package (Production Edition) › and look for devkit schematic and check the clock conf.
It is expected observation as you're supplying wrong clock source. The design works fine with 125MHz and you've confirmed it as well. Hence, I shall go ahead and close the case.
I now transition this thread to community support.
If you have a new question, feel free to open a new thread to get the support from Altera experts.
Otherwise, the community users will continue to help you on this thread.
Regards,
Pavee