Frozen image from Comcast TV

I live in Chicago, IL. 

I have Comcast Limited Basic.

I have two TVs. For each TV, I use a Comcast DTA (digital-to-analog adapter) to get Comcast TV. The Comcast TV signal comes into the DTA, and the signal travels from the DTA to the TV via an HDMI wire.

Sometimes, the following happens:

I turn on the TV. A frozen image comes on and stays on. That image may be from some TV program that I watched days ago. After I change the channel, the TV is "unfrozen" and works properly.

So, what is going on here? How do I fix this situation?

Thank you.