It's definitely an issue with jsreports to chromium, but i don't know what it would be. If i run my docker to a bash shell and then execute
/app-rprt$ /usr/bin/chromium-browser --no-sandbox --disable-dev-shm-usage --headless --disable-gpu --print-to-pdf $1
it generates output.pdf with content in it. This is the output though.
[0322/121710.387637:ERROR:bus.cc(399)] Failed to connect to the bus: Failed to connect to socket /var/run/dbus/system_bus_socket: No such file or directory
[0322/121710.391744:ERROR:bus.cc(399)] Failed to connect to the bus: Failed to connect to socket /var/run/dbus/system_bus_socket: No such file or directory
[0322/121710.391805:ERROR:bus.cc(399)] Failed to connect to the bus: Failed to connect to socket /var/run/dbus/system_bus_socket: No such file or directory
[0322/121710.400029:WARNING:bluez_dbus_manager.cc(247)] Floss manager not present, cannot set Floss enable/disable.
[0322/121710.441692:WARNING:sandbox_linux.cc(393)] InitializeSandbox() called with multiple threads in process gpu-process.
659 bytes written to file output.pdf
Not sure if that matters or not in what you guys are doing with the return. I did not run your docker to see what the output looks like on your side. Could you please let me know if you think this is the issue?