I have the exact same problem it is sooooo frustrating and takes ages to get connection and program back. I too plug in through hdmi powered by plug point, was struggling to understand any other way of powering!
Only bought mine October when it was fine, it has been happening for about 3 weeks now and everything else in the house is ok.
Same thing, my nowtv stick worked fine for ages, then about 6 months ago started losing connection.
Tried everything and ended up buying a new stick as I figured the old one had just broken.
New one does same thing within seconds.
Contacted Vodafone as I then thought it must be the Internet.
They changed me to a static ip.... Same thing happens. So frustrating.
What have you done now TV???
Something has changed.
Here's another similar thread where the forum member is also on Vodafone has their ISP.