Created attachment 117354 [details]
Example output for failed marking as read for mails

SUMMARY

I switched to the SQLite backend. On the console, I saw that there occur DATABASE ERRORs named " Parameter count mismatch". One example is when I try to mark a large set of mails as read. This didn't work, so I guess the corresponding query failed. I'm attaching two examples.

Googling, I saw that this error occurred elsewhere in Qt code using SQLite:

https://www.qtcentre.org/threads/30220-Using-bound-values-in-insert-gives-quot-parameter-count-mismatch-quot-error-in-SQLite
https://stackoverflow.com/questions/20786003/qt-qsqlquery-bindvalue-works-with-but-not-with-placeholders
https://stackoverflow.com/questions/24684550/qt-5-with-sqlite-bindvalue-results-in-parameter-count-mismatch-error 

It may be that the same type of bug occurs in akonadi. In that case, this issue may be a relatively easy one to fix.


SOFTWARE/OS VERSIONS

Akonadi version: 18.08.3
KDE Plasma Version: 5.14.3 
KDE Frameworks Version: 5.52.0
Qt Version: 5.11.1


ADDITIONAL INFORMATION

Despite the failed queries, the SQLite backend seems to function well.