In the Chrome DevTools tab I can see that from time to time the client tries to load http://localhost:8080/sw.js which fails with 404.
In my setup the tomcat is behind an apache server which forwards to the tomcat. From outside the correct url would be http://myserver/sw.js. Why is the client trying to load sw.js with the internal url.
Well at some point it probably has been and some code has asked it to be registered. If you are not using a service worker, the quick fix would be to delete it in dev tools/applications and see if it reappears