I sometimes get these errors
akonadi_kolab_resource_1(14984)/libakonadi Akonadi::ProtocolHelper::streamPayloadToFile: Wrote 4292 bytes to "/home/chrigi/.local/share/akonadi/file_db_data/5693967_r5"
Payload file "/home/chrigi/.local/share/akonadi/file_db_data/5693969_r4" could not be open for reading!
Error: "No such file or directory"
Revision r4 is indeed gone from disk, and r5 is available, the question is what tries to read the old revision after it's gone.