Cannot login to C. 6.13 after Jira upgrade to 8.10 (all self-hosted / user directories problem)

[Henjo Völker]

Dear community,

so our company had Jira 7.X and Confluence 6.13 running for a long time now. We recently decided to upgrade Jira to the newest version, new license and all. We didn't feel a need to upgrade Confluence at the moment, though. So our Jira runs at 8.10 now. All self-hosted.

After the upgrade, some users, including mine, weren't able to login to C. anymore. Generic error message that just says something along 'Couldn't log you in, try again' (it's in German so I don't know the exact English message).

As we are quite a small company, I got access to an admin account for troubleshooting. I checked everything and found that the users seem to have been synced from Jira. Now we do have several customers that have access to our Jira, but not to C. at all. This is how it's meant to be.

Under user directories I found a "Jira Server" directory and the "Confluence Internal Directory" one. So I checked the users: The customers are only in the Jira Server directory, while our internal users additionally are members of the Confluence Internal Directory. Obviously, only these can login to C.
My user and also another employee's, however, is not a member of the latter anymore. I don't know why, nobody else knows, nobody actively removed me from there, and I can't add anyone to this directory again. I even tried disabling Jira user management/sync, but no luck.

Can anyone help me with this issue?

Thanks in advance.

[JiraJared]

Hey Henjo,

It sounds like Confluence is connected to Jira for user management. 
When you hit sync in Confluence on the Jira user directory, does it work? Or fail?

Also can you check that the users in Jira have the confluence-users group because without it, they won’t be able to log into Confluence.

Let me know how you go!

[Henjo Völker]

Hi, thank you very much for reaching out.

• The sync fails. It says I should check some logs on the server. I don't have access to this but a co-worker has. I can ask him, but he's really busy at the moment which means this will take some time.
• There is no confluence-users group in our Jira groups management. Should I create one? Does it have to be called exactly like this to work? Or won't it work if it isn't automatically created?
• Also, the authentication between J & C is apparently "deprecated" / "outdated" but the troubleshooting links all lead to some crappy "404 not found" pages on Atlassian.

[JiraJared]

Henjo,

Try this. Change the password for the Application under User Directories in Jira, then use that same password on Confluence to get the sync back up and running. 
Once it’s working, then we can see if users can log in. It may be that the Jira groups were applied in Confluence 

[Henjo Völker]

OK unter user directories in Jira there is nothing but the "Jira Internal Directory". It says I can't change this one as long as I'm logged into it. Naturally, all users we have are logged in via this directory.

There is no password option here. If I click the edit button, I can only activate some layered-groups-function which I don't think I need.