I am having issues with lip sync on the ps3 app. The words are being spoken 1-2 seconds before the mouth moves on the actors. It is very annoying. I am connected with a HDMI cable and use wireless connection. The sound is through thd tv speaker, no soundbar etc connected.
I have no issues with other apps and I can play online games no problem.
This is bit of a long shot, but have you tried rebooting both your PS3 and your router to see if there is any improvement ?
I would switch back on your router first then followed by your PS3.
Suppose there is no harm in trying, the only other thing i would possibly suggest is signing out of the App, then remove it from the PS3 and try re installing the NowTV App once again (make sure you know your username and password before logging out of the App).
I don't use a PS3, so these are just general suggestions on my part.
It only seems to happen during films. I have uninstalled and re-installed but it's just the same. LG tv from 2011 has the Nowtv app available to download yet Panasonic from last year doesnt have the app available for download. Available apps on devices should be in the description imo, but that is another story.