cant connect to remote smb

A problem that arrived a some time ago, but only now getting round to trying to fix it.

Set-up

A remote Diskstation with an <name>.i234.me configured because we have no fixed ip.

My windows pc, at home. Only remote connections

My macbook which was connected through smb://<name>.i234.me

For the macbook

This worked for a while, then at a certain moment i had to reconnect the smb everytime

and now i can only connect when I'm in the same network as the diskstation, but not remote

The windows pc still flawlessly connects remote. So serverside nothing changed.

Connecting through

cifs://<name>.i234.me

afp://<name>.i234.me

smb://<external ip address>

Doesn't work

Any tips?