Sorry about that.
When admin email is set, lshttpd should only keep the latest 10 core files, we will reduce it to 5. Sometime the core file is just too big to be sent in a email. changing the core file directory is a good idea.
If you don't mind please send us the core files you have for analysis, at least the back trace from the email.
Please make sure that the "Log Level" has been set to "DEBUG" at server level and vhost level, otherwise you will not see any debug message in the log.
Thank you for your help.