for example Note:This is being done using ISPCONFIG API I add 20 domains in 1st attempt. No Error I add 20domains again 2nd attempt No Error I add 20domains again - Error the exampledomain has not sent any data, ERR_EMPTY_RESPONSE what could be the reason for this, where I can check, what is causing this?
Might be that you use a security addon like mod_evasive in apache or a firewall that has a DOS attack detection that blocks you because you do too many requests too fast. Check web server global error and access.logs and try to remember which additional security software you might have installed on your server that may block fast https requests.
