I have done a bit of port-forwarding before with success, but suddenly I encountered this problem that I do not know how to solve. I am hosting a samba share on port 137-139 and 445, and accessing the device via its local IP address (192.168.x.x) address works fine -- I can view the shares.
However, when I port-forward the correct ports in my router from the correct local IP address and access it via my public IP address, it works fine; but when anyone else tries to, the ports look closed. No online port scanner, nor friends I have contacted can connect to the share or see the open ports, even when using the exact same commands as me and my public IP. I am guessing my router supports hair-pinning since I can access my public IP at all times, but why would it behave differently for me compared to anyone else when using my public IP address?
My router model is ASUS RT-AC85P and I am hosting the share on a Raspberry Pi 3 Model B+. I have been able to port-forward before, so it is not a problem with my ISP, rather my router since I relatively recently changed it.