In a setup where GlusterFS snapshots are browsed to list previous versions of a directory, it says "There are no previous versions available". Following is the configuration:

# testparm -s
Load smb config files from /usr/local/etc/samba/smb.conf
Loaded services file OK.
Weak crypto is allowed
Server role: ROLE_STANDALONE

# Global parameters
[global]
	clustering = Yes
	load printers = No
	log file = /usr/local/var/log/samba/log.%I
	netbios name = GFS-SMB-CLUSTER
	security = USER
	server string = Samba Server
	idmap config * : backend = tdb


[gluster-vol]
	comment = For samba share of volume vol
	kernel share modes = No
	path = /
	read only = No
	vfs objects = shadow_copy2 glusterfs
	shadow:format = _GMT-%Y.%m.%d-%H.%M.%S
	shadow:snapprefix = ^s[A-Za-z0-9]*p$
	shadow:sort = desc
	shadow:basedir = /
	shadow:snapdir = /.snaps
	glusterfs:loglevel = 7
	glusterfs:logfile = /usr/local/var/log/samba/glusterfs-vol.%M.log
	glusterfs:volume = vol

As a side effect snapshot directories are not browsable from SMB clients: 

# smbclient \\\\192.168.122.101\\gluster-vol -U anoopcs%smb
Try "help" to get a list of possible commands.
smb: \> cd .snaps\
smb: \.snaps\> ls
  .                                   D        0  Thu Nov 12 10:44:49 2020
  ..                                  D        0  Wed Nov  4 16:11:30 2020
  snap_GMT-2020.10.09-09.48.22        D        0  Fri Oct  9 15:17:41 2020
  snap_GMT-2020.10.12-11.05.59        D        0  Fri Oct  9 15:17:41 2020

		1044984 blocks of size 1024. 970284 blocks available
smb: \.snaps\> cd snap_GMT-2020.10.12-11.05.59
cd \.snaps\snap_GMT-2020.10.12-11.05.59\: NT_STATUS_FILE_IS_A_DIRECTORY
smb: \.snaps\> exit

Steps to reproduce:
1. Have a GlusterFS-Samba setup
2. Create some files and directories
3. Create and activate snapshots using `gluster` command line utility
4. Try to list Previous versions by right clicking on directories.

Additional info:
[2020/11/11 16:04:59.437798, 10, pid=99412, effective(1001, 1001), real(1001, 0)] ../../source3/smbd/open.c:813(fd_open)
  fd_open: name .snaps/snap_GMT-2020.10.12-11.05.59, flags = 0200000 mode = 00, fd = -1. Is a directory
[2020/11/11 16:04:59.437840,  5, pid=99412, effective(1001, 1001), real(1001, 0)] ../../source3/smbd/open.c:4534(open_directory)
  open_directory: Could not open fd for .snaps/snap_GMT-2020.10.12-11.05.59 (NT_STATUS_FILE_IS_A_DIRECTORY)
. . .
[2020/11/11 16:04:59.438458, 10, pid=99412, effective(1001, 1001), real(1001, 0)] ../../source3/smbd/open.c:5854(create_file_unixpath)
  create_file_unixpath: NT_STATUS_FILE_IS_A_DIRECTORY
[2020/11/11 16:04:59.438489, 10, pid=99412, effective(1001, 1001), real(1001, 0)] ../../source3/smbd/open.c:6046(create_file_default)
  create_file: NT_STATUS_FILE_IS_A_DIRECTORY