Post Comments Disappearing

We switched a website from Drupal to WordPress recently, and for some reason, when comments are posted, they appear for a brief period of time, and then disappear. They’re shown in the Dashboard, they’re approved, but they still don’t show up on their respective posts.

I’ve tried changing template tags, changing settings, repairing the comments table, adding indexes to the comments table, disabling plugins, and a lot of other miscellaneous bug fixes I found on related WordPress forums.

This is urgent and needs to be resolved ASAP. Thanks in advance for your help!