As mentioned the bug still exists in chromium 67.0.3396.87 from the Debian Repo. I setup a totally fresh VM for this purpose running stretch.
There I downloaded the source and compiled following the instructions at . Upstream Chromium 69 worked fine so I tried to compile the exact same version as installed by APT on my notebook 67.0.3396.87 including  into my workflow.
The 67.0.3396.87 version from upstream didn't have the issue. For testing I used a plain mp3 served by python's SimpleHTTPServer:
python -m SimpleHTTPServer
First I always had the sandbox issue, I could start the upstream-versions only with --no-sandbox. Afterwards I tried to also compile the sandbox and start chromium using the wrapper. But this should not be relevant here
Then I found out that the error also occurs when I used the Debian Package on my dedicated VM. After runnig it via CLI I also got this Error Message: