indexer: Error: conn unix:indexer (pid=562491,uid=10003): didn't reply with a valid VERSION line

Hi,

A few weeks ago we moved our mailserver to a new location. On the new location we use now dovecot v2.3.19.1 insteadof v2.3.4.1. We moved the mailboxes by zipping all mailbox on the old location and unzip on the new location.

Now we see an indexer error quite often:

indexer: Error: conn unix:indexer (pid=563158,uid=10005): didn't reply with a valid VERSION line: 1 0 indexer indexer

Sometimes when we try to use the index for searching we just get no results.

We can't really find a cause for this error on the internet. As solution we found "Just do a re-indexing." Ok, but what may cause this error? And how can we prevent this error in the future?

As indexer we use lucene.

Any hint is appreciated.

Phren