JSON Response not working in 11.5.3 HF2

We have an iRule that was working in 11.4.0 HF4. Now that we have upgraded to 11.5.3 HF2, our vendors are receiving timeouts from us. The iRule is simply to send back the ASM support ID. Below is the iRule that was given to us that should have worked, but this also started the timeouts.

when HTTP_REQUEST {
      if { [HTTP::uri] contains "rest" }  { set rest_content 1
                log local0. "HTTP REQUEST REST DETECTED"
    } else {
        set rest_content 0
}
    }
when ASM_REQUEST_BLOCKING
      {
       log local0. "ASM REQUEST BLOCK:  REST DETECTED= $rest_content"
       if { $rest_content }
       {
        set response "REST Page blocked"
        ASM::payload replace 0 [ASM::payload length] ""
        ASM::payload replace 0 0 $response
        HTTP::header replace Content-Length [ASM::payload length]
       }
      }
when ASM_RESPONSE_VIOLATION
{
   set x [ASM::violation_data]
   log local0. "ASM-SUPPORT-ID: [lindex $x 1 ]"
   set error "[lindex $x 1 ]"
   if {([lindex $x 0] contains "VIOLATION_HTTP_STATUS_IN_RESPONSE")}
   {
      set response "{\"returnStatus\":false,\"returnCodedMessage\":[{\"code\":\"WebService.SystemError\",\"message\":\"The requested operation was rejected. Please consult with your administrator. Your support ID is: $error \"}],\"returnMessage\": []}"
      ASM::payload replace 0 [ASM::payload length] ""
      ASM::payload replace 0 0 $response
      HTTP::header replace Content-Length [ASM::payload length]

}
}