I've been a virginmedia customer for 3/4 years and had this problem initially then it went away for no apparent reason.
It's back with vengeance though I haven't changed any hardware or how I use the TV. I have to restart the box every night if I want the audio back in sync. It's extremely annoying and the only reason I'll consider leaving when my contact is up next.
I've tried "Dolby to PCM" various times and it makes zero difference. (It will be out of sync again by the next evening) The hdmi is plugged in to an ARC slot (whatever that means)
It would be annoying but less of an inconvenience if the box didn't take an age to restart ☹️
By logging out do you mean simply switching back to regular virgin tv channels? If so then the audio sync issue persists - I can't be sure if regular tv channels cause it or apps but it might be worth trying regular tv only for a day or two to see if the problem doesn't start