Load Balancing IIS Servers

Might be SNI

You can you use either different Server SSL profiles or a generic irule like 

when HTTP_REQUEST
{
    set serverSideSSLSNIName [ string tolower [HTTP::host] ]
}

when SERVERSSL_CLIENTHELLO_SEND
{
	#https://support.f5.com/csp/article/K41600007
	if { [ info exists serverSideSSLSNIName ] }
	{
	    if { [catch { SSL::extensions insert [binary format SSScSa* 0 [expr { [set sni_length [string length $serverSideSSLSNIName]] + 5 }] [expr { $sni_length + 3 }] 0 $sni_length $serverSideSSLSNIName] } ] }
	    {
		    log local0. "ERROR: Attempting to assign server SSL  - SNI : $serverSideSSLSNIName failed"
	    }
	}
}