Yes my log is also flooded to death with this error since upgrade to 6.11. For me, it's occuring when my blue iris server (separate bare metal win 10 PC) tries to run cleanup (move files to archive or delete files past max retention).
Oct 1 01:15:12 RackServer smbd[6050]: [2022/10/01 01:15:12.387938, 0] ../../source3/smbd/files.c:1193(synthetic_pathref) Oct 1 01:15:12 RackServer smbd[6050]: synthetic_pathref: opening [bistore/livingroomcam.20220924_011246860.jpg] failed
In smb extras I have the following
[global]
server min protocol = SMB3_11
client ipc min protocol = SMB3_11
force user = nobody
force group = users
I also have several ZFS shares there but the camera storage relating to this error is on the unraid array, on a normal share set up via unraid gui. The share is fine in windows explorer on the same PC. It all worked fine on Unraid 6.10.3.
Happy to provide further info if it might help