alepensato
My apologies, after re-reviewing the code this seems to be used only if you don't provide a Search Base. At this point I'm not sure what's going on in your case. I tried again but still unable to replicate your issue. I'm hoping someone more verse with LDAP and O-style trees can pop in and provide more input because at this point I'm unsure what your issue is. Error 32 indicates issues with DN, Search User, access/permission issues, etc. so that's about all the suggestions I have based on guides/posts online.
Maybe one of these will help?
I am using OpenLDAP (and MSAD) with DC-style trees so this could be the disconnect where yours isn't working as you are using O-style trees. I've never seen this style before here so that's the only thing I can think of at this time. I know you are going to say "but it's working for agents" but Agents use a different auth method than Users. With Users it goes through an additional lookup and sync process:
If you want you can either unpack the plugin or download the raw plugin files and add debug statements and mess with the code yourself to see where it's failing and why. All I can go on is the logs you've provided which simply states Error 32 which isn't that helpful.
Cheers.