There has been a change in the way logs are managed from EHX 8.7 and above.
Logs are still stored in the SDF file and the period before being overwritten is set in the App Config file (see solution: Matrix: The Matrix event logs are written to the EHX PC, when ever the user starts the EHX application).
The logs in the SDF file are now swept out every 24 hours and placed in the location:  C:\Users\***Username***\AppData\Roaming\Clearcom\EHX Configuration System\logs
These text files are permanently stored and have to be manually deleted if desired. There are two types of logs here. Those labelled dd-mm-yyyy.log are exceptions logs from EHX. An example of an exception in EHX is when a logic maestro macro references anon-existent control and the map fails to build. A dialogue box appears and this is logged as an exception.
The other type of logs, labelled EHX Event Log dd-mm-yy.txt are the matrix event log files.  The sweeps occur every 24 hours (approximately) from when EHX is opened and only occur when EHX is open. Furthermore, remember to start event log to ensure logs are being taken.

The daily sweep removes all logs older than x where x is defined by a registry key:

AdmMessagesKeepPeriod

Possible values:

Week

Day

Month

When a save diagnostics zip file is taken, the event log is composed from the SDF file. The logs in AppData can be used to supplement this to provide information on a historical event.

Note: if you are using EHX client /server mode, then you need to collect the log files from the Server PC