Why am I having this kind of error .Warning: validateDOMNesting(…): cannot appear as a descendant of

i’m creating big project with React js/Redux, smth like social media app. I don’t know from where, however I got the error index.js:1 Warning: validateDOMNesting(...): <a> cannot appear as a descendant of <a>. at a. I don’t know how to solve that, because it is not showing where the error is. I have changed all my -s to NavLink, but the error didn’t solved. Help me if you can.