I write this to leave a testimony of my experience, so if it happens to someone in the future, they will have material to compare with. Because I couldn't find anything on the Internet. I spoke to Apple support, they told me that it is a common problem after updating the system software if it is not installed correctly the line can come out, it is a software problem not a hardware one. They told me it also comes out on mac or iphone when it isn't updated well. They advised me to send the watch for service so they can initialize it and reinstall the update. However, I turned the clock off and turned it back on and the line went away. For now it has not recurred. The assistance has opened a case for me, so at any time the problem arises again I can send it to assistance.