AppleTV 4K connects at 720p automatically to a 1080p HDTV

Ever since a recurring series of power disruptions that left my Sony Bravia system messed-up, I have had to connect my AppleTV 4K directly to my 1080p HDTV via HDMI cable. Before I connected directly to the TV, when the AppleTV 4K was connected through the receiver to the TV, the AppleTV would automatically connect at 1080p; now, with a direct HDMI connection, the AppleTV 4K defaults the connection to 720p when it is initially turned on daily and I need to manually enter settings and change the video to 1080p, which the AppleTV then accepts and connects to the TV at that resolution.

Does anyone have any idea why this is happening or what can be done to correct this? Is there some way to permanently set the resolution output to 1080p, rather than having to do this every time I watch programming through the AppleTV?

Thanks.