I've found a bug in NXTI. Adding new traps works fine, but when you try to edit one it returns multiple Query errors:

This Nagios XI nstallation is an upgrade from and old version, and uses postgresql for the nagiosxi database. It seems that this bug is related to that, since AFAIK postgresql doesn't support "LIMIT 1" statements on update queries.
NXTI component version is 1.0.1, XI version is 5.5.7.
Thanks, Gonzalo