Sorry for the delay in response to this, yesterday slipped by me.
In good news, I know we have a lot in version 1.4.0 that is focused around submissions and nominations, and I'm hoping it's A) released soon B) fixes the problems you're having with randomness.
That said, it's really hard to know what's going on here based on the details currently provided, and I understand it can be difficult to provide more details with a seemingly random thing.
Does your admin user always receive some sort of notification that a nomination was submitted? Do the nominations always show up in the admin list, despite not always appearing to have worked from the frontend like when there is no "Nomination saved successfully" message?