After applying visual deflicker sometimes the Visual Previews phase fail. I know that the visual deflicker should re-load after applying deflicker, but it does not and I cannot playback the sequence with the Visual Previews tool turned on.

I have a feeling that it tryes to run in the background, cause when I try to close the program it says:
"Batch processing still active!"
"You still have background tasks running. Do you really want to abort those tasks?"

However, I've let LRT run for some time to eventually finish the hidden task, but it does not.

This is done in the Long Term Workflow with LRT 5.1.1

Logfile sent on e-mail.

The log file that you've sent me is full or errors concerning your DNG files. Which files are those? Directly created by a camera or converter with Adobe DNG Converter? In any case something is failing when creating the visual previews from those files. You can see that for yourself in the log. Try a shorter sequence, try restarting Computer/LRT and try again. Check the log and see if this happens in any case.