Ran into an odd issue yesterday in which I had a Backup Copy job failing and stating it could not connect to the storage. Long story short, I had changed the mount server on the repository that I was pulling the backups from to a 2016 physical server I had built specifically so my REFS partitions would mount for FLRs. This was only supposed to be a mount server so I never hooked it into my backup network.
I changed the mount point on the backup repository back to a server that had access to the repository and this resolved the issue. With identifying the cause I went ahead and added the mount server to the backup network so it could see the repositories.
My question is .... shouldn't the GFS be like any other job and use the gateway to determine which proxy it will use to pull the backup out of the repository. Seemed kinda odd to me and didn't make sense. Also I am sure others may run into this if they tried to get around the whole REFS 3.1 / FLR mount issue when using 2012r2 backup servers.