P: Hanging on launch (Mac 10.14.6)

I am having the same exact problem with 10.14.6 and 8.4. I tried to remove the preferences file and that made no difference. So I launched from a simple catalog that I had used in a test a few months ago and then created a new catalog and tried to import my current catalog into the new catalog. It said creating new temporary catalog only to hang. I waited about an hour and then hit the cancel button and Lightroom then said cancelling for about another hour. I eventually did a Force Quit even though the system did not say Lightroom was unresponsive. Reading above I don't have the Logitech plug-in so that is not the issue. Very frustrating.

Having the same issue. Reverting Lightroom is not helping for me. On MacOS 10.14.6, iMac (Retina 5k, 27-inch, 2017). Tried 8.3.0, 8.3.1 and 8.4. All get the spinning beachball when attempting to import. Resetting prefs did not change the behavior. 

I totally agree. I don't have time for testing... I am working on the latest iMac and latest OS - like millions of other users - so I would expect LRC to be compatible. 
I waisted a few hours on Sunday trying to resolve something that should have been working in first instance. 

Thanks for the reply.
Desperately flailing trying to fix computer problems seems to be becoming the new default mode with every OS, app and firmware update these days. Brings back painful memories of the bad old days, when every other day was a BSD adventure..
Thinking about the Logitech Options issue further, I wonder if removing the LogiOptionsAdobe folder was the only route open for those folks dealing with a LR installation that permanently froze whenever they tried to open LR.

I am also wondering if the next LogiOptions update will repopulate the CEP extensions directory.

Because I have a basic desktop setup and don't use customized keyboard/mouse settings in LR or PS, I am also wondering whether I would be better off just removing the entire LogiOptions app from my system.

The problem is figuring out why you're seeing it and others aren't. That takes a bit of detective work.

You don't happen to have that same Logitech plug-in installed, do you? It's been known to cause problems in the past.

All this is very interesting but why are we all jumping through so many hoops to try and solve a problem which is the responsibility of Adobe. I suspect we are only the tip of an iceberg!
Rikk cannot something not be done about this?

I wasn't sure if that "check" that happens during the Reading Preferences step was looking to the folder. Also because I was desperately flailing about trying to fix my problem and I read that someone else had done that for a different problem.  

Disabling the Logitech Options plugin (using the Plugin Manager in LR) appears to have cured the problem.  Many thanks to David Golding and MACKIE for the tip!
MACKIE, I am curious why you also removed the LogiOptionsAdobe folder from the Adobe CEP extensiions Common Files subdirectory.

Link to the forum issue is: https://forums.adobe.com/thread/2646582

If it is any help, I had this issue on Windows with LR hanging at startup and the problem ended up being the result of a Logitech plugin.  Not sure how this translates to the Mac but might provide some insight:

OK - I have had this same problem since the Windows update and tried everything without success.  Finally, finally, fixed it.

There is a folder inside

C:\Program Files\Common Files\Adobe\CEP\extensions: LogiOptionsAdobe

I dragged that folder out of the directory structure. 

I also saw that there is a Plugin in the Lightroom Plugin Manager for LogiOptions, and I disabled it.

Everything is back to normal now!!!

Hope this helps someone before they remove all their preferences and settings and plugins.