I'm pretty sure you read this one before? But just in case that not... here you go:
NDI Network guidelines
Did you also tried 1080p30 ?
What kind of cables do you use and how long are they ?
Did you use CAT spookys anywhere in your system?
As Oaktown said before, there are so many potential weak spots in your system. My very first intention would be AFTER I really really know that all my Network settings are right ... Change all the 10 Gbit CAT wires... with the highest grade cables I could get (Cat7). Or at the very very least....test all your network wires with a good CAT tester... NOT a CAT beeper. More something similar to this: www.pockethernet.com