[PROBLEM]
I have a known-to-be-working smb.conf which shares a local folder with write-access for certain logins, and read-only access for guests/anonymous.
Authenticated login (using a smbpasswd-mapped account) works.
The config is known to be stable and working on many hosts (in my setups), but on one machine, I got strange errors and timeouts - although the samba logs say authentication as guest/nobody okay.
Long story short:
A parent (!) folder of the shared path, on the samba host had permissions set to "700" (rwx --- ---).
This made it impossible for the `nobody` user (=which is the unix account samba guests operate as) to access the shared (sub-folders).
[SOLUTION]
Fixing the access permissions to "775" (which were the correct and expected ones), solved the issue!