What's configured under Preferences / Labels / Label Assignments (and In Specific Folders below it, if applicable)?
Is there anything there which would take a long time to calculate (e.g. filters based on file contents)?
Do any folder tabs point to network shares that don't exist or are not accessible?
Similarly, is anything on your toolbars or Favorites pointing to such shares? (Or using icons that live on them.)
Is the problem only happening when particular folders are read?
Does it happen each time, or only the first time after a restart or similar?
Any scripts installed? Does the problem still happen if they're disabled?
Timing might be tricky if it only lasts a couple of seconds, but if you can generate some process snapshots while the delay is happening, we can hopefully use those to see what's happening during that time. Here's how to make them: