https://elgg.org/discussion/view/3269582/error-creating-admin-user-during-installation   

I installed through FTP as it is a hosted domain and only happens when I go to the admin dashboard.  I'm now wondering if there's an issue with the path, which I'll look into, but I'd assume that the paths are defined correctly as the rest of the site is working absolutely fine.  Odd.  I've used many previous versions of Elgg in a previous job and I've seen many problems but never this one.  

Thanks for the help, @mariano and @nikolai

Got it!

There was a path and permissions issue that seemed to have not worked in the install so I fixed it manually.  All looks good for now!

If anyone else has these problems with an FTP install, I'd absolutely check all relative and absolute paths are correct and permissions have been assigned properly, even if you think you've done it once already (some changes don't always stick!).

Yes and maybe that's the reason why my site is slow as I mentioned in  https://elgg.org/discussion/view/3267628/elgg-4-became-slower

Confirmed.

Try to enable this option in elgg-config/settings.php:

$CONFIG->simplecache_enabled = true;

Thank you that helped!!! I wonder, what is the reason for this? Is it a bug? Everything was working fine in elgg 3