After wasting about 20 hours with no success. Here is my situation:
I had working OMV 3 on HDD (still have it as backup solution). Remote ssh, web admin etc. through dynamic DNS + port forwarding worked, but I used only VPN to get in and used other services locally.
I have decided to upgrade to OMV 4 from blank putting it on second HDD if anything goes wrong. I rather deal with known problems with new setup, then deal with problems on upgrade which I don't have experience width.
I have problem to get response from server back out on OMV 4.
I assume router is ok, as all works with OMV 3. Using "online port forwarding testers" to OMV 3 setup, ssh port access is OK, VPN say is closed, but I can get connection successfully using my phone from the outside for VPN to OMV 3.
On OMV 4 VPN access doesn't work, nor access to SSH, or OMV admin web through dynamic address + port forwarding.