I ran into this issue as well, and wrote up the specifics with what I’m encountering in Container (non-root) user can't write to /dev/stdout or /dev/stderr. What’s weird there is:
echo "hi"
works, but:
echo "hi" >> /dev/stdout
fails with a permission denied, which contradicts the comment in Allow non-root users to write to stdout/stderr - #5 by jerome.