Sonatype Nexus web publishing ends up in Error 404

We want to publish a Sonatype Nexus NPM repository behind our sophos UTM. so far all works docker, apt, apk, maven and most of npm and yarn.
But some URLs of npm repositories contains a leading "@" which ends up in an 404 error. As we cannot find any Rule ID we have no clue how to get that working. We hope to find a hint here how to get it working.

Here is the error log:

2024:12:17-11:33:31 fw-XXXXXXX httpd: id="0299" srcip="Client IP" localip="Public IP" size="196" user="-" host="Client IP" method="GET" statuscode="404" reason="-" extra="-" exceptions="-" time="306" url="/repository/npm-npmjs-org/@jridgewell/sourcemap-codec" server="nexus.XXXXX.YYY" port="443" query="" referer="-" cookie="-" set-cookie="-" websocket_scheme="-" websocket_protocol="-" websocket_key="-" websocket_version="-" uid="Z2DxC1vDjKkL-cfXiBpfZgAAADY"

How to test:

curl -v 'nexus.XXXXX.YYY/.../@jridgewell/sourcemap-codec'
curl -v 'nexus.XXXXX.YYY/.../sourcemap-codec'

npm -dd install @jridgewell/sourcemap-codec