There are repeatable messages of the below type that appear in the Event logs of the Administration and Monitoring Console:
SQLite: unable to open database file
This error is related to the training tasks/processes when multiple versions of document definition are applied to documents within the training batch, and there are many documents within this batch as well.
This error has no actual drawbacks and is fixed starting from FC18.104.22.16813 (the latest release with the fix included always can be downloaded from https://www.abbyy.com/flexicapture-downloads/distributed-invoices/). It will be also required to update all the training batches to the latest version after the upgrade of FlexiCapture12.
Please note that we strongly recommend making backups of the important data before performing the update.