Unplug the sound bar from the power socket.
Now go to your aerial cables. If they're the molded type, unplug and reconnect. If they're ones with the DIY-fit coax plugs, check the fitting of the plug to the cable.
Next, go online and find out which your local transmitter is and what RF channel or frequency is used for your HD muxes.
Do a manual tune just for the affected muxes. if there's enough signal then they'll tune in and add themselves to the existing channel rosta. But where there's still a problem with them then at least you won't lose your SD channels.
Channel lose can vmbe cause by lots of issues. Where some new bit of gear has been introduced, it could be something as simple as disturbing the cables which is enough to tip the balance on something that's already close to marginal.
Poorly shielded fly leads can be a surprising weak point. Those molded ones that used to come free with VCRs and that can be bought cheapish front supermarkets and corner shops are a bit of a liability with digital TV signals. They're also prone to breaking at the solder joint in the plug ends. Because it's all shrouded in plastic you can't tell, and it can get just a hairline fracture where you get some channels but not all. Give the cables a wiggle when in manual tuning mode to see if the signal level fluctuates.
Another cause for signal anomalies is interference from modern power supplies known as swith mode power supplies. Better quality coax fly leads will generally help or even completely cure that.
Thanks. 
