KMail not displaying everything

Hello list,

I've just taken the latest upgrade of KMail in the hope that the new version 
would fix a problem I've had for a week or two, but it hasn't.

Often, selecting a message doesn't cause it to be displayed; the message pane 
stays as it was. And images are not being shown at all: just place holders - 
and no, I haven't changed the user setting.

Running akonadictl fsck and vacuum found nothing and has made no difference. 
Archiving the folder affected seems to work ok.

Is this a known problem?

-- 
Regards,
Peter.

Gentoo testing system, openrc-0.42.1
gcc 10.2.0, sys-kernel/gentoo-sources 5.4.92
QT 5.15.2, KDE frameworks 5.78.0, KDE plasma 5.20.5
KDE apps 20.12.2 incl KMail 5.16.2 (20.12.2), akonadi 20.12.2
dev-db/mariadb-10.5.8, net-libs/webkit-gtk-2.30.4
x11-base/xorg-drivers-1.20