How long has this been happening ?
If it's only been recently, check this website below if there is any planned schedule engineering maintenance work on the TV transmitter or repeater in your area.
Are you also using any Y splitter or sharing the incoming TV aerial with any other Freeview TV devices ?
Have you tried a full factory reset to see if that makes any difference ?
If you have already tried a full blown factory reset (where you had to re enter all your details once again) then you could try a forced software update on the smart box by pressing the Home button x 5 on the RC, quickly followed by pressing the FF x 3, quickly followed by pressing RW x 2 which should open a secret screen and select update software, even if you are on the current version.
Some smart box owners have reported that a Y splitter might help, where the box sometimes latches onto a weaker TV transmitter when the aerial is connected directly into the smart box (my only concern is that you are reporting loss of all TV channels and not a reduced number of TV stations).
Hopefully, other helpful members on here will offer you some further guidance on things to try.
What app/Channel are you trying to watch?
you could try the uninstall /re install apps BBC iPlayer/Now TV/Tv player or anyother with live TV.
As Roku devices do not support input from an antenna, you must have this confused with an ethernet lead have you checked the connection to your router, or tried using Wifi?