dovecot.index.pvt reset, view is now inconsistent

Problem solved by going in manually. The log message appears for empty "public" folders. Say, you have a folder X with subfolder Y, where X does not contain any e-mail. The log message disappears if you drop an email into X, then remove it. Puf, gone! So, there seems to be a baby bug in how dovecot manages the index in this case.