DAOS catalog cannot be updated

I have upgraded 4 of our production servers to Domino 8.5 during the last 2 weeks and yesterday I enabled DAOS on one machine. Occasionally I see the following entry on the console

Unfortunately, this is the only hint that something seems to be wrong. But I cannot locate the problem. It would be great if an error message could be more verbose and says where the exact problem is. I’m running 3 parallel compact tasks at the moment.

Despite of this error message the compact task works fine and more and more data is written to the DAOS repository.