I've imported all my email and folders from Thunderbird into Kmail 5.14.1.
But all that's ended up in Kmail is the emails with titles but no body, which is useless.
The import has included the individual inboxes for each of my email accounts. The single email in each of those displays complete, with title and body.
In Thunderbird I don't have a separate set of folders for each account. I use the Local Folders inbox for all then delete/move as I receive/sort them to my own set of folders.
Anyone know how I import the complete emails for all my other folders?

FOUND THE ANSWER!!
Uninstalled Kmail.
It's the most convoluted, illogical, difficult and user unfriendly email client in existence. Help is useless and ancient, no one interested in providing support.
I'll stay with Thunderbird, or install Evolution.