No luck, looks like something with this version is not quite ok:
Summary
[D] unknown:0 - Start sync requested for profile: “caldav-sync-60”
[D] unknown:0 - Removing queued profile change sync due to sync trigger: “caldav-sync-60”
[D] unknown:0 - Synchronizer::getBackUpRestoreState
[D] unknown:0 - Starting sync with profile “caldav-sync-60”
[D] unknown:0 - Disable sync on change: false false
[D] unknown:0 - Starting oop plugin “caldav-sync-60”
[D] unknown:0 - Starting process “/usr/lib/buteo-plugins-qt5//oopp/caldav-client” with plugin name “caldav” and profile name “caldav-sync-60”
/usr/lib/buteo-plugins-qt5//oopp/caldav-client: symbol lookup error: /usr/lib/buteo-plugins-qt5//oopp/caldav-client: undefined symbol: _ZN5Buteo11SyncResults16staticMetaObjectE
[D] unknown:0 - Process “/usr/lib/buteo-plugins-qt5//oopp/caldav-client” started with pid 3997
[D] unknown:0 - Process “/usr/lib/buteo-plugins-qt5//oopp/caldav-client” with pid 3997 was unable to register DBus service: “com.buteo.msyncd.plugin.profile-caldav-sync-60” | “com.buteo.msyncd.plugin.caldav-sync-60”
[D] unknown:0 - Client plug-in runner initialized
[D] unknown:0 - New network state: true New type: “WLAN” ( 2 )
[D] unknown:0 - Network status:
[D] unknown:0 - Online:: true
[D] unknown:0 - Connection:: 2
[D] unknown:0 - sync-ui dbus interface is getting called
[D] unknown:0 - Sync session started
[D] unknown:0 - ClientPluginRunner started thread for plugin: “caldav-sync-60” , returning: true
[D] unknown:0 - attempt to start sync session due to network session opened succeeded.
[D] unknown:0 - Sync status changed for account “60”
[W] unknown:0 - Invalid reply for init from plugin
[W] unknown:0 - Could not initialize client plugin: “caldav”
[D] unknown:0 - Sync running for 60
[D] unknown:0 - Process “/usr/lib/buteo-plugins-qt5//oopp/caldav-client” finished with exit code 127
[W] unknown:0 - Invalid reply for getSyncResults from plugin
[D] unknown:0 - Session finished: “caldav-sync-60” , status: 3
[D] unknown:0 - Clean up session for profile “caldav-sync-60”
[D] unknown:0 - Stopping the OOP process for “caldav”
[D] unknown:0 - Sync status changed for account “60”
Especially this line:
/usr/lib/buteo-plugins-qt5//oopp/caldav-client: symbol lookup error: /usr/lib/buteo-plugins-qt5//oopp/caldav-client: undefined symbol: _ZN5Buteo11SyncResults16staticMetaObjectE