The DB-API high-level abstractions for Zabbix and the Zabbix server contain some invalid asserts, which contain code with side-affects and which isn't executed on a -DNDEBUG build (which is the default build argument on Gentoo). This leads to random segfaults due to the use of unitialized values. The attached patch file fixes the corresponding assert()s to have the actual code outside of the assert, and leaves only the test in the assert. I haven't checked whether this is already fixed in 2.0.4, but couldn't find any other mention on the JIRA for these kind of segfaults.
Incidentally, zabbix_server (at the same version) used to work fine for us, and only after an upgrade of the base system (which meant a restart of the server process) led to the random segfaults occuring.