Saowaluk,
FYI, we’ve been actively engaging our Basis team (TREX support) and they’re working closely with SAP to address the issue.
The TREX search issue on NAPP which we’ve experienced is due to huge memory utilization which exceeded the maximum memory defined.
Basis team has made some configuration changes to minimize this issue. 
In addition, there’s a revision version of TREX which should address the memory leak issue which is planned for installation.
I understand that it’s frustrating to experiences outages on NAPP / CHAPP.
We do hope that users will continue to use NAPP so we’re putting the real load to the system.
We will keep you posted once the TREX revision fix has been installed.
Currently, TREX is up running fine for APP.