The syslogs for the Kiwi Syslog web access are stored in SQL Compact database files. First you will want to check the setup, and make sure you are still logging to Syslog Web Access. Please see below:
If web access is enabled, remember that there is a 4GB limit on the SQL Compact database. If you have a high volume of syslogs the database may be full, and need to clear itself out.