I also noticed the same problem, disqus comments don’t sync to wordpress. This problem started for my blog last June 14, 2016, when I was using the official disqus plugin. Manual syncing does not help, it just appears to run indefinitely.
After finding DCL two days ago, I replaced the official disqus plugin with it and I’m very happy, but still, syncing does not work.
Anyway, I would like to share some of my findings, which are not being answered in the support section of the official disqus plugin.
One thing I noticed is there are a lot of duplicate custom fields “dsq_needs_sync” in most of my posts (you have to enable custom fields under screen options to see this), although I’m not sure this is related to the syncing problem. I already checked and there are more than 400,000 rows in the table post_meta where meta_key is “dsq_needs_sync” and has a value of “1”. Very few are null.
I suspect the cron for syncing comments is adding these each time it runs, so I disabled syncing for now. Comments from disqus still appear okay at the frontend. The only problem is syncing to the backend in wordpress does not work.
Do you guys think this has anything to do with the syncing problem?