What version of nikkalite? They have a printable one, and a screenprint version that "works" with latex and solvent
I've done a few rolls through our solvent... But about 100 through our latex this year... Not one issue with the latex printing, not sure if they have issues with solvents or you got a bad batch... But nikkalites been great for us. And about 1/3 the price of 3m 5100.... but again, were on latex so maybe they're having solvent issues.
Can you post some pictures? It might help diagnose the issue, especially if it's happening on two different media's. Is it all colors or specific? Could be a bad batch of ink.... Are you using OEM ink? You ruled out the media so I'd look into the ink. Heat shouldn't be an issue.