I collected some information that might help with debugging, unfortunately some output uses German localization, I can translate these if needed:
In the shell where I started akonadi with akonadictl start, I got this output (many lines duplicated and removed for brevity): "Das Objekt existiert nicht am Pfad »/org/freedesktop/NetworkManager/ActiveConnection/2«" [...] org.kde.pim.kimap: Connection to server lost QAbstractSocket::HostNotFoundError [...] QIODevice::write (QSslSocket): device not open org.kde.pim.kimap: Connection to server lost QAbstractSocket::NetworkError org.kde.pim.kimap: Connection to server lost QAbstractSocket::NetworkError org.kde.pim.kimap: Connection to server lost QAbstractSocket::HostNotFoundError org.kde.pim.kimap: Connection to server lost QAbstractSocket::HostNotFoundError [...] "Das Objekt existiert nicht am Pfad »/org/freedesktop/NetworkManager/ActiveConnection/2«" [...] QIODevice::write (QSslSocket): device not open org.kde.pim.kimap: Connection to server lost QAbstractSocket::RemoteHostClosedError org.kde.pim.kimap: Connection to server lost QAbstractSocket::NetworkError [...] "Das Objekt existiert nicht am Pfad »/org/freedesktop/NetworkManager/ActiveConnection/2«" [...] QIODevice::write (QSslSocket): device not open "Das Objekt existiert nicht am Pfad »/org/freedesktop/NetworkManager/ActiveConnection/2«" [...] QIODevice::write (QSslSocket): device not open org.kde.pim.akonadiserver.search: Executing search "kontact-2268689595-SearchSession" org.kde.pim.akonadiserver.search: Search "kontact-2268689595-SearchSession" done (without remote search) org.kde.pim.akonadiserver.search: Executing search "kontact-2268689595-SearchSession" org.kde.pim.akonadiserver.search: Search "kontact-2268689595-SearchSession" done (without remote search) org.kde.pim.akonadiserver.search: Executing search "kontact-2268689595-SearchSession" [...] org.kde.pim.akonadiserver: QueryBuilder::exec(): database reported transaction timeout, retrying transaction org.kde.pim.akonadiserver: "Lock wait timeout exceeded; try restarting transaction QMYSQL3: Der Befehl konnte nicht ausgeführt werden" org.kde.pim.akonadiserver: QueryBuilder::exec(): database reported transaction timeout, retrying transaction org.kde.pim.akonadiserver: "Lock wait timeout exceeded; try restarting transaction QMYSQL3: Der Befehl konnte nicht ausgeführt werden" stracing akonadiserver shows this for example: [pid 110942] write(10, "\1\0\0\0\0\0\0\0", 8) = 8 [pid 110942] poll([{fd=10, events=POLLIN}, {fd=26, events=POLLIN}, {fd=28, events=POLLIN}, {fd=36, events=POLLIN}, {fd=38, events=POLLIN}, {fd=42, events=POLLIN}, {fd=47, events=POLLIN}, {fd=52, events=POLLIN}, {fd=61, events=POLLIN}, {fd=69, events=POLLIN}, {fd=76, events=POLLIN}, {fd=77, events=POLLIN}, {fd=79, events=POLLIN}, {fd=86, events=POLLIN}, {fd=89, events=POLLIN}, {fd=90, events=POLLIN}, {fd=95, events=POLLIN}, {fd=96, events=POLLIN}, {fd=99, events=POLLIN}, {fd=100, events=POLLIN}, {fd=110, events=POLLIN}, {fd=114, events=POLLIN}, {fd=116, events=POLLIN}, {fd=121, events=POLLIN}, {fd=122, events=POLLIN}, {fd=125, events=POLLIN}, {fd=126, events=POLLIN}, {fd=129, events=POLLIN}, {fd=132, events=POLLIN}, {fd=136, events=POLLIN}, {fd=142, events=POLLIN}, {fd=146, events=POLLIN}, ...], 46, 48) = 1 ([{fd=10, revents=POLLIN}]) [pid 110942] read(10, "\2\0\0\0\0\0\0\0", 16) = 8 [pid 110942] poll([{fd=10, events=POLLIN}, {fd=26, events=POLLIN}, {fd=28, events=POLLIN}, {fd=36, events=POLLIN}, {fd=38, events=POLLIN}, {fd=42, events=POLLIN}, {fd=47, events=POLLIN}, {fd=52, events=POLLIN}, {fd=61, events=POLLIN}, {fd=69, events=POLLIN}, {fd=76, events=POLLIN}, {fd=77, events=POLLIN}, {fd=79, events=POLLIN}, {fd=86, events=POLLIN}, {fd=89, events=POLLIN}, {fd=90, events=POLLIN}, {fd=95, events=POLLIN}, {fd=96, events=POLLIN}, {fd=99, events=POLLIN}, {fd=100, events=POLLIN}, {fd=110, events=POLLIN}, {fd=114, events=POLLIN}, {fd=116, events=POLLIN}, {fd=121, events=POLLIN}, {fd=122, events=POLLIN}, {fd=125, events=POLLIN}, {fd=126, events=POLLIN}, {fd=129, events=POLLIN}, {fd=132, events=POLLIN}, {fd=136, events=POLLIN}, {fd=142, events=POLLIN}, {fd=146, events=POLLIN}, ...], 46, 47) = 0 (Timeout) [...] [pid 110942] read(89, "\3\0\0\0\0\0\0\0u\0\20\0\0\377\377\377\377\377\377\377\377\0\0\0\0\1\0\0\0\25\0\0"..., 70) = 70 [pid 110942] write(10, "\1\0\0\0\0\0\0\0", 8) = 8 [pid 110942] ppoll([{fd=89, events=POLLIN|POLLOUT}], 1, {tv_sec=30, tv_nsec=0}, NULL, 8) = 1 ([{fd=89, revents=POLLOUT}], left {tv_sec=29, tv_nsec=999996833}) [pid 110942] write(89, "\3\0\0\0\0\0\0\0\365\0\0\0\0\377\377\377\377", 17) = 17 [pid 110942] write(10, "\1\0\0\0\0\0\0\0", 8) = 8 [pid 110942] poll([{fd=10, events=POLLIN}, {fd=26, events=POLLIN}, {fd=28, events=POLLIN}, {fd=36, events=POLLIN}, {fd=38, events=POLLIN}, {fd=42, events=POLLIN}, {fd=47, events=POLLIN}, {fd=52, events=POLLIN}, {fd=61, events=POLLIN}, {fd=69, events=POLLIN}, {fd=76, events=POLLIN}, {fd=77, events=POLLIN}, {fd=79, events=POLLIN}, {fd=86, events=POLLIN}, {fd=89, events=POLLIN}, {fd=90, events=POLLIN}, {fd=95, events=POLLIN}, {fd=96, events=POLLIN}, {fd=99, events=POLLIN}, {fd=100, events=POLLIN}, {fd=110, events=POLLIN}, {fd=114, events=POLLIN}, {fd=116, events=POLLIN}, {fd=121, events=POLLIN}, {fd=122, events=POLLIN}, {fd=125, events=POLLIN}, {fd=126, events=POLLIN}, {fd=129, events=POLLIN}, {fd=132, events=POLLIN}, {fd=136, events=POLLIN}, {fd=142, events=POLLIN}, {fd=146, events=POLLIN}, ...], 46, 51) = 1 ([{fd=10, revents=POLLIN}]) [pid 110942] read(10, "\2\0\0\0\0\0\0\0", 16) = 8 [pid 110942] poll([{fd=10, events=POLLIN}, {fd=26, events=POLLIN}, {fd=28, events=POLLIN}, {fd=36, events=POLLIN}, {fd=38, events=POLLIN}, {fd=42, events=POLLIN}, {fd=47, events=POLLIN}, {fd=52, events=POLLIN}, {fd=61, events=POLLIN}, {fd=69, events=POLLIN}, {fd=76, events=POLLIN}, {fd=77, events=POLLIN}, {fd=79, events=POLLIN}, {fd=86, events=POLLIN}, {fd=89, events=POLLIN}, {fd=90, events=POLLIN}, {fd=95, events=POLLIN}, {fd=96, events=POLLIN}, {fd=99, events=POLLIN}, {fd=100, events=POLLIN}, {fd=110, events=POLLIN}, {fd=114, events=POLLIN}, {fd=116, events=POLLIN}, {fd=121, events=POLLIN}, {fd=122, events=POLLIN}, {fd=125, events=POLLIN}, {fd=126, events=POLLIN}, {fd=129, events=POLLIN}, {fd=132, events=POLLIN}, {fd=136, events=POLLIN}, {fd=142, events=POLLIN}, {fd=146, events=POLLIN}, ...], 46, 50) = 0 (Timeout) [...] [pid 110942] read(89, "\3\0\0\0\0\0\0\0u\0\20\0\0\377\377\377\377\377\377\377\377\0\0\0\0\1\0\0\0\25\0\0"..., 70) = 70 [pid 110942] write(10, "\1\0\0\0\0\0\0\0", 8) = 8 [pid 110942] ppoll([{fd=89, events=POLLIN|POLLOUT}], 1, {tv_sec=30, tv_nsec=0}, NULL, 8) = 1 ([{fd=89, revents=POLLOUT}], left {tv_sec=29, tv_nsec=999996833})