Thank you for your feedback Michael.We don't use reverse lookups, neither in the access control rules of OpenLDAP, nor at the TCP wrapper level.
I'd already checked the OpenLDAP changes history. I agree we use a somewhat old OpenLDAP version, but I didn't find any obvious clue of a bug that could induce such freezings in more recent versions.
Anyway, upgrading is often an action to consider at least ..