Created attachment 121410 [details]
Backtrace

Created attachment 121411 [details]
akonadictl fchk result

Copying the relevant bt here:

[KCrash Handler]
#6  QString::~QString (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/c++/9/bits/atomic_base.h:326
#7  Akonadi::Server::Query::Condition::~Condition (this=0x7f260c214db8, __in_chrg=<optimized out>) at /usr/src/debug/akonadi-server-19.04.2-188.3.x86_64/src/server/storage/query.h:77
#8  0x0000556a6d01f454 in QVector<Akonadi::Server::Query::Condition>::destruct (this=<optimized out>, to=0x7f260c214de8, from=0x7f260c214de8) at /usr/include/qt5/QtCore/qvector.h:356
#9  QVector<Akonadi::Server::Query::Condition>::freeData (x=0x7f260c214d70, this=<optimized out>) at /usr/include/qt5/QtCore/qvector.h:553
#10 QVector<Akonadi::Server::Query::Condition>::~QVector (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/qt5/QtCore/qvector.h:72
#11 Akonadi::Server::Query::Condition::~Condition (this=<optimized out>, __in_chrg=<optimized out>) at /usr/src/debug/akonadi-server-19.04.2-188.3.x86_64/src/server/storage/query.h:77
#12 0x0000556a6d01f454 in QVector<Akonadi::Server::Query::Condition>::destruct (this=<optimized out>, to=0x7f260c5a7d18, from=0x7f260c59d9f8) at /usr/include/qt5/QtCore/qvector.h:356
#13 QVector<Akonadi::Server::Query::Condition>::freeData (x=0x7f260c597d10, this=<optimized out>) at /usr/include/qt5/QtCore/qvector.h:553
#14 QVector<Akonadi::Server::Query::Condition>::~QVector (this=<optimized out>, __in_chrg=<optimized out>) at /usr/include/qt5/QtCore/qvector.h:72
#15 Akonadi::Server::Query::Condition::~Condition (this=<optimized out>, __in_chrg=<optimized out>) at /usr/src/debug/akonadi-server-19.04.2-188.3.x86_64/src/server/storage/query.h:77
#16 0x0000556a6d01fc6c in QVector<Akonadi::Server::Query::Condition>::destruct (this=<optimized out>, to=0x7f260c0b3838, from=0x7f260c0b3838) at /usr/include/qt5/QtCore/qvector.h:356
#17 QVector<Akonadi::Server::Query::Condition>::freeData (x=0x7f260c0b37f0, this=0x7f262fffe240) at /usr/include/qt5/QtCore/qvector.h:553
#18 QVector<Akonadi::Server::Query::Condition>::~QVector (this=0x7f262fffe240, __in_chrg=<optimized out>) at /usr/include/qt5/QtCore/qvector.h:72
#19 Akonadi::Server::Query::Condition::~Condition (this=0x7f262fffe240, __in_chrg=<optimized out>) at /usr/src/debug/akonadi-server-19.04.2-188.3.x86_64/src/server/storage/query.h:77
#20 Akonadi::Server::QueryBuilder::~QueryBuilder (this=0x7f262fffe230, __in_chrg=<optimized out>) at /usr/src/debug/akonadi-server-19.04.2-188.3.x86_64/src/server/storage/querybuilder.h:45
#21 0x0000556a6d04d90f in Akonadi::Server::ItemFetchHelper::buildFlagQuery (this=0x7f262fffe760) at /usr/src/debug/akonadi-server-19.04.2-188.3.x86_64/src/server/handler/itemfetchhelper.cpp:220
#22 0x0000556a6d051030 in Akonadi::Server::ItemFetchHelper::fetchItems(std::function<void (Akonadi::Protocol::FetchItemsResponse&&)>&&) (this=this@entry=0x7f262fffe760, itemCallback=...) at /usr/src/debug/akonadi-server-19.04.2-188.3.x86_64/src/server/handler/itemfetchhelper.cpp:413
#23 0x0000556a6d04bc78 in Akonadi::Server::ItemFetchHandler::parseStream (this=0x7f260c062440) at /usr/include/c++/9/bits/std_function.h:398
#24 0x0000556a6d01b7be in Akonadi::Server::Connection::handleIncomingData (this=0x556a6dd27f10) at /usr/include/c++/9/bits/unique_ptr.h:357
#25 0x00007f26620bd6b2 in QtPrivate::QSlotObjectBase::call (a=0x7f262fffe930, r=<optimized out>, this=<optimized out>) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:394
#26 QSingleShotTimer::timerEvent (this=0x7f260c004cd0) at kernel/qtimer.cpp:318
#27 0x00007f26620b1255 in QObject::event (this=0x7f260c004cd0, e=<optimized out>) at kernel/qobject.cpp:1282
#28 0x00007f266208566f in doNotify (event=0x7f262fffea60, receiver=0x7f260c004cd0) at ../../include/QtCore/../../src/corelib/kernel/qobject.h:142
#29 QCoreApplication::notify (event=0x7f262fffea60, receiver=0x7f260c004cd0, this=<optimized out>) at kernel/qcoreapplication.cpp:1141
#30 QCoreApplication::notifyInternal2 (receiver=0x7f260c004cd0, event=0x7f262fffea60) at kernel/qcoreapplication.cpp:1065
#31 0x00007f26620db0ab in QTimerInfoList::activateTimers (this=0x7f260c0044f0) at kernel/qtimerinfo_unix.cpp:643
#32 0x00007f26620db924 in timerSourceDispatch (source=<optimized out>) at kernel/qeventdispatcher_glib.cpp:183
#33 0x00007f2660617b33 in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0
#34 0x00007f2660617dc0 in ?? () from /usr/lib64/libglib-2.0.so.0
#35 0x00007f2660617e4f in g_main_context_iteration () from /usr/lib64/libglib-2.0.so.0
#36 0x00007f26620dbcd1 in QEventDispatcherGlib::processEvents (this=0x7f260c000b20, flags=...) at kernel/qeventdispatcher_glib.cpp:423
#37 0x00007f26620842eb in QEventLoop::exec (this=this@entry=0x7f262fffeca0, flags=..., flags@entry=...) at ../../include/QtCore/../../src/corelib/global/qflags.h:140
#38 0x00007f2661ebcf91 in QThread::exec (this=<optimized out>) at ../../include/QtCore/../../src/corelib/global/qflags.h:120
#39 0x00007f2661ebe112 in QThreadPrivate::start (arg=0x556a6dd25a00) at thread/qthread_unix.cpp:360
#40 0x00007f266128efaa in start_thread () from /lib64/libpthread.so.0
#41 0x00007f2661b2f71f in clone () from /lib64/libc.so.6

Could you please start Akonadi by running

    akonadictl start --verbose

and attach ~/.local/share/akonadi/akonadiserver.error file to this report after the server crashes? Thanks

Dear Bug Submitter,

This bug has been in NEEDSINFO status with no change for at least
15 days. Please provide the requested information as soon as
possible and set the bug status as REPORTED. Due to regular bug
tracker maintenance, if the bug is still in NEEDSINFO status with
no change in 30 days the bug will be closed as RESOLVED > WORKSFORME
due to lack of needed information.

For more information about our bug triaging procedures please read the
wiki located here:
https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging

If you have already provided the requested information, please
mark the bug as REPORTED so that the KDE team knows that the bug is
ready to be confirmed.

Thank you for helping us make KDE software even better for everyone!

I finally removed some mails popping up shortly before the issue and now the issue is solved for me. Feel free to close this, if the needed info is needed to track down the issue as it will not be possible for me anymore to provide these information.