This used to be broken when using wired connections on the LAN and you try to access port forwarded services through the WAN IP of the router. I opened a few tickets with MSI on this (#1095517, #1090749, #1090749). With firmware 723375, it looks like they have now made WiFi connections consistent with this behaviour as well.
MSI support initially told me that they don't support MacOS because I was emailing from a MacBook. Then they told me they don't support Unix when I explained these are services hosted on Linux servers with port forwarding on the router to these services. Then I pointed out that the PlayStation OS is BSD based which is technically Unix so their comment about not supporting Unix does not make sense if they are marketing their router as gaming router. I also reproduced the issue on a Windows machine connected directly to the router and gave them the instructions using out of the box windows tools to reproduce the issue. Then they told me the MSI router is a gaming router and gamers don't need this functionality so MSI does not support it. MSI support suggested I return the router and buy one from some other manufacturer. I explained to them that the return period has long expired so that is not an option for me anymore and that people buy gaming routers expecting that it will meet their needs such as this especially since old routers from 5-10-15 years ago have supported this setup without issue. In the end they decided to close the tickets as an unsupported setup and not needed for gamers.
I recommend you contact MSI support about this issue as well so that they can see that there are many people that expect this to work. This is a very normal setup for the main router in a house that has gaming as well as other services running through the same router. MSI support even suggested I have a different router for those services separate from gaming which makes no sense when you have one internet connection with your ISP. I really hope this issue gets fixed because it is embarrassing to explain to the family that the "new" fancy router is why they can't get their email on their phones when they are at home but if they go off WiFi, they can access their email that is hosted on the LAN.
[UPDATE] Port forwarding from outside my LAN works for me on firmware 723375. This evening I setup Split DNS to handle the LAN traffic trying to access the port forwarded services as well. With this setup, I don't need to downgrade the firmware.
