We've identified an issue where the latest libpthread library versions are not compatible with Firebird 2.5 (including the latest available release of vanilla version 2.5.9.27139 and HQbird 2.5 till the version 2.5.9.27173). Fix for HQbird 2.5 is already available (in the version from April 10).
See details here:
https://ib-aid.com/articles/problem-with-libpthread-library-in-linux-installation-of-2.5