Are you referring to the “Devtools failed to load SourceMap” messages? Those always appear and can be ignored.
https://wiki.appstudio.dev/Solutions_to_Common_Problems#.22Chrome_can.E2.80.99t_find_.2A.min.map.22
Tip: If you’re pasting code, html or config files, surround it by triple back ticks (```) and it will be fomattted properly.