nas542 access from WLAN to "myname.zyxel.me" not working

Hey guys,

I have a weird issue. I am using the nas542. The access to the NAS IP wia WLAN has worked from day one from any device (and still works). After some tweaking also the access to "myname.zyxel.me" works from other networks (for example from my mobile phone internet connection or from work) but what does not work ist the acces to "myname.zyxel.me" from my own LAN (for any device connected to my WLAN or plugged in the router via network cable). The issue is not device specific, the same happens for windows, ubuntu or android devices. 
Any idea what might cause this issue?

Cheers,
Alex

#NAS_Apr_2019