That's what I did all the time with the results posted already.

I tried using your proposed command.
What happens now is the following:

1. using my mobile phone connected through Wifi to my local network with VPN on (assuming that even the local traffic routes through the VPN then, but could be wrong)
2. I can connect to the Grafana server using 10.147.17.36:4000 in Safari with success
3. tail -f /var/log/syslog shows traffic coming through

4. now I disable VPN and switch Wifi off
5. enable VPN again and try to connect to 10.147.17.36:4000 through mobile network 4G (ipv4)
6. syslog showing:
Apr 12 10:07:35 TakuMoe_Open_Pi grafana-server[636]: t=2019-04-12T10:07:35+0200 lvl=info msg="Request Completed" logger=context userId=0 orgId=0 uname= method=GET path=/ status=302 remote_addr=10.147.17.35 time_ms=5 size=29 referer=
Apr 12 10:07:35 TakuMoe_Open_Pi grafana-server[636]: t=2019-04-12T10:07:35+0200 lvl=info msg="Request Completed" logger=context userId=0 orgId=0 uname= method=GET path=/login status=302 remote_addr=10.147.17.35 time_ms=42 size=24 referer=
7. but no luck connecting to the grafana. All I see is "Error The request timed out: http://10.147.17.36:4000/" on my mobile browser

---