SUMMARY
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When selecting a specific email on a akonadi maildir ressource, kmail shows "Unable to retrieve item from ressource: [LRCONFLICT] Ressource akonadi_maildir_ressource_14 tries to modify item 325379 () (in collection 54) with dirty payload, aborting STORE."
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STEPS TO REPRODUCE
1. Open folder on akonadi maildir ressource
2. Select specific email

OBSERVED RESULT
kmail shows "Unable to retrieve item from ressource: [LRCONFLICT] Ressource akonadi_maildir_ressource_14 tries to modify item 325379 () (in collection 54) with dirty payload, aborting STORE." and the content of mail is not shown (stays on content previous.

EXPECTED RESULT
Email content is displayed, no warning.

SOFTWARE/OS VERSIONS
Kmail version: Version 5.18.1 (21.08.1)
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 5.22.5
KDE Frameworks Version: 5.86.0
Qt Version: 5.15.2

ADDITIONAL INFORMATION
It seems clearing the cache/reindexing using akonadiconsole helps for a while.
I think there is a bug in akonadi maildir ressource causing wrong database entries.