Error when set collaborator
I get this error when a user is set in collaborator but in admin and editor it works fine
This seems to have a problem with
https://github.com/joshp23/YOURLS-AuthMgrPlus/blob/475417ff91807d7020fa3dc3b3150bfb6b1607e7/authMgrPlus/plugin.php#L380
Your log is saying that the column user does not exist, and that column is referred to in the above code.
That column is added to the table on plugin activation
https://github.com/joshp23/YOURLS-AuthMgrPlus/blob/475417ff91807d7020fa3dc3b3150bfb6b1607e7/authMgrPlus/plugin.php#L486-L509
Check to see if the user column exists in your table and if not, try disabling and re-enabling the plugin. IF it still doesn't exist, add it manually if you must, but error logs are helpful as well.
If the user column is there when you check, I'm really not sure what the problem is, as I cannot reproduce the problem.