OS X randomly asking for NAS login after using mount_afp on Terminal
Might want to check /etc/auto_afp for your mount point and remove if present.
Sounds like your Mac is constantly trying (and retrying) to automatically mount that share unsuccessfully.

Try moving to using autofs so you don't need to manually deal with mounting your share and it should be seamlessly unmounting that share when you change networks: http://blog.grapii.com/2015/06/keep-network-drives-mounted-on-mac-os-x-using-autofs/

As for Photos requesting you mount your AFP share despite the Photos Library being stored locally I also don't have a clue there.
Maybe changing how its mounted as suggested may resolve your issue? I'll try and recreate your environment here and let you know if I have the same problem (with a possible solution).