I have two ROKU Express boxes getting hot and I am losing closed caption and I am hearing impaired, so CC means a lot to me.
I can unplug to cool boxes down and CC will work again for a while. I have replaced the HDMI cord and the power box with the cord and still have the same problem. I have changed the location of the box and set box on a rag hoping to help remove heat but that did not work either.
I don't think heat has anything to do with you losing CC. What are you watching when this happens? When it happens on one can you switch to the other (hopefully cooler) device and see if it's occurring on the same program/video?