Thanks for trying those things. That rules out some of the possible causes.
Some other things to try:
[ul][li]If you delete all the collections again, and then create a new, empty collection (when in the Collections folder, click the New Folder button), do you get a delay when going into that empty collection?
If not, what if you manually drag a .txt file into the collection, then fully exit Opus (via File / Exit Directory Opus) and then re-launch Opus and go tot he collection? Does the .txt file show up in the collection without delay?
[/li]
[li]Do you have any scripts installed? (Preferences / Toolbars / Scripts.) If so, try disabling them.
[/li]
[li]To test if the problem is related to your configuration or toolbars, backup your current configuration (Settings > Backup & Restore), then completely uninstall Opus, reboot, and reinstall it. You'll now be using the default settings and toolbars. Does the problem still happen? (After testing, you can restore the config backup via the same menu, but be sure to do the test before restoring anything.)
[/li]
[li]If none of those things make a difference, it would seem to be something external to Opus. That could include antivirus causing a small operation that should be fast to be very slow (e.g. blocking Opus from reading the collection XML data while it takes a long time to scan it or similar), or 3rd party shell extensions (ShellExView can list them) or even things like video codecs (Icaros, which is included in some codec packs, has caused some strange problems recently). Those are all things which get loaded into the Opus process outside of our control, and can cause almost anything if not well behaved.[/li][/ul]