The two databases (old and new) are on the same server.

The recovery model is always simple (and any problem here would result in high disk activity).

There is no...

Thanks, we will look at the locks when next it happens. The other causes (reindexing, stats, growing files) would entail disk activity though, wouldn't they, which is a missing symptom.

There are no inline functions. We even had the problem with a plain "insert into newdb.dbo.table(...) select ... from olddb.dbo.table"