Why is my Roku overriding my Leaf external antenna?

Good morning.

I have a Roku connected to an external antenna for local channels.

When my television is connected to the internet, I lose a bunch of local channels. This morning, our internet was offline and suddenly they were all back. The minute the internet reconnected however, they were gone again. I have scanned and rescanned channels multiple times and nothing.

The signal on these channels is strong so that isn't the issue. 

I have a Sharp mode LC-50LBU591U. Software version 13.0.0 build 24062-38 that says it is updated.

Any ideas gang?

Thanks-Lynette