I have the same problem here, but nobody knows the solution.
There are import job commands that you have to reset it via Rails Console, but I have not found the right one.
With these two following commands you can start the import jobs via Rails Console, you have to execute them one after the other. But it only works once, when it’s done you can’t start the job via web interface again.
1: job = ImportJob.create(name: 'Import::Ldap', payload: Setting.get('ldap_config'))
2: job.delay.start