That’s something i’ve noticed as well. Jayne is currently presenting Nine’s special news coverage of Remembrance Day and even when she read the intro of the bulletin, she was smiling and looked like she was trying to restrain herself from laughing. It isn’t acceptable IMO.
I’m going to be honest, I don’t think Jayne’s as good of a presenter as what is often suggested on here. She does have good newsreading skills, no doubt, but she isn’t one of the best at the network.