Unable to retrieve item from resource: [LRCONFLICT]

[Peter Humphrey]

Hello,

I just joined this list on Thursday, two days ago. A week ago I created a new 
user for myself and set it up. I created my kmail folders and imported my 
filters, but did not import any messages. I have one POP3 account with my ISP 
and one IMAP4 account to pick up local network mail. Until joining this list 
everything was going well; new messages were received from both accounts and 
filtered into the right folders.

However, two messages from this list have caused problems. In both cases, 
kmail said "Unable to fetch item from backend (collection -1) : Unable to 
retrieve item from resource: [LRCONFLICT] Resource ak..." on the status bar at 
the window bottom.

I wanted to see what was wrong with the message, so I moved all the others to 
another folder and then looked in .local/share/local-mail/.Linux.directory/
KDE-PIM/new (and .../cur and .../tmp) but there was nothing to be found.

What does LRCONFLICT mean? I dare say it means Local Resource Conflict, but 
what does it imply? And does a collection -1 really exist?

The filter that moves messages into that folder is:

[Filter #5]
Applicability=0
AutomaticName=true
ConfigureShortcut=false
ConfigureToolbar=false
Enabled=true
StopProcessingHere=true
ToolbarName=<List-Id>: kde-pim.kde.org
action-args-0=51
action-name-0=transfer
actions=1
apply-on=check-mail,manual-filtering
contentsA=kde-pim.kde.org
fieldA=List-Id
funcA=contains
identifier=jdvFTLV3wpmKeZ2c
name=<List-Id>: kde-pim.kde.org
operator=and
rules=1

What should I do to recover from this, and perhaps offer more info?

-- 
Regards,
Peter.

Gentoo stable system, openrc-0.41.2
gcc 8.3.0, sys-kernel/gentoo-sources 4.19.66
QT 5.12.3, KDE frameworks 5.60.0, KDE plasma 5.15.5
KDE apps 19.04.3 incl KMail 19.04.3 (5.11.3), akonadi 19.04.3
dev-db/mariadb-10.2.22-r1, net-libs/webkit-gtk-2.24.2
x11-drivers/xf86-video-amdgpu 19.0.1
dev-libs/amdgpu-pro-opencl 19.10.785425-r1