SUMMARY
Since last update Kmail/ Akonadi fails to get new email from IMAP server. Kmail reports "failed to append item" when synchronising mailbox. The Akonadi error log states: 
2021-08-09T14:00:17 [CRITICAL] org.kde.pim.akonadiserver: DATABASE ERROR:
2021-08-09T14:00:17 [CRITICAL] org.kde.pim.akonadiserver:   Error code: "1292"
2021-08-09T14:00:17 [CRITICAL] org.kde.pim.akonadiserver:   DB error:  "Incorrect datetime value: '2021-08-09T12:00:17Z' for column `akonadi`.`pimitemtable`.`datetime` at row 1"
2021-08-09T14:00:17 [CRITICAL] org.kde.pim.akonadiserver:   Error text: "Incorrect datetime value: '2021-08-09T12:00:17Z' for column `akonadi`.`pimitemtable`.`datetime` at row 1 QMYSQL: Unable to execute query"
2021-08-09T14:00:17 [CRITICAL] org.kde.pim.akonadiserver:   Values: QMap((":0", QVariant(int, 0))(":1", QVariant(QString, "6773"))(":2", QVariant(QString, ""))(":3", QVariant(QString, ""))(":4", QVariant(qlonglong, 21))(":5", QVariant(qlonglong, 3))(":6", QVariant(QDateTime, QDateTime(2021-08-09 12:00:17.471 UTC Qt::UTC)))(":7", QVariant(QDateTime, QDateTime(2021-08-09 12:00:17.471 UTC Qt::UTC)))(":8", QVariant(bool, false))(":9", QVariant(qlonglong, 2491777)))
2021-08-09T14:00:17 [CRITICAL] org.kde.pim.akonadiserver:   Query: "INSERT INTO PimItemTable (rev, remoteId, remoteRevision, gid, collectionId, mimeTypeId, datetime, atime, dirty, size) VALUES (:0, :1, :2, :3, :4, :5, :6, :7, :8, :9)"
2021-08-09T14:00:17 [WARN ] org.kde.pim.akonadiserver: Error during insertion into table "PimItemTable" "Incorrect datetime value: '2021-08-09T12:00:17Z' for column `akonadi`.`pimitemtable`.`datetime` at row 1 QMYSQL: Unable to execute query"
2021-08-09T14:00:17 [WARN ] org.kde.pim.akonadiserver: Error while handling command CreateItem on connection akonadi_imap_resource_0 (0x559fee8e4a30)
2021-08-09T14:00:26 [INFO ] org.kde.pim.akonadiserver: Subscriber "MessageViewerMonitor - 94908118964128" disconnected
2021-08-09T14:00:26 [INFO ] org.kde.pim.akonadiserver: Subscriber "MessageListTagMonitor - 94908119944352" disconnected
2021-08-09T14:00:26 [INFO ] org.kde.pim.akonadiserver: Subscriber "KMail Kernel ETM - 94908118071664" disconnected
2021-08-09T14:00:26 [INFO ] org.kde.pim.akonadiserver: Subscriber "SpecialCollectionsMonitor - 94908118206576" disconnected
2021-08-09T14:00:26 [INFO ] org.kde.pim.akonadiserver: Subscriber "FilterManagerTagMonitor - 94908124039120" disconnected
2021-08-09T14:00:26 [INFO ] org.kde.pim.akonadiserver: Subscriber "TagActionManagerMonitor - 94908124186832" disconnected


This even happens with a completely new user set up. The directory structure as present on the IMAP server is correctly created in KMAIL upon setup, but retrieving messages fails with the above error. 

STEPS TO REPRODUCE
1. Try to get new mail from imap server


OBSERVED RESULT
KMAIL states "failed to append item" and does not show emails coming in upon sync; as a result all email folders are empty and stay empty when setting up as a new user.

EXPECTED RESULT
Emails actually show up in Kmail

I´ĺl happily create any logfile or anything else you need to squash this ugly bug

OS: OpenSuse Tumbleweed
KDE:5.22.4
KDE Framework: 5.84.0