expect script reporting an issue 'alloc: invalid block: 0x1d614b0: 30 1 Aborted (core dumped)'

Here is my sample expect script, that reporting the above error. Please take a look and let me know if any issue with this. I'm suspecting issue with expect_before block. Is there any limit to expect_before block? Also, one strange thing noticed is when I added pipe '|' after string like "Connection Refused"| it is working fine though it is part of trial and error.

#!/usr/bin/expect
spawn sftp {sample_hostname} 
set timeout 30
gets stdin password
expect_before {
  "(yes/no)" {
  send "yes
  "
  exp_continue
  }
  "Connection Refused" {
  exit 1 }
  "not found." {
  exit 2 }
  "Permission denied" {
  exit 3 }
  " Could not resolve hostname" {
  exit 4 }
  "REMOTE HOST IDENTIFICATION HAS 
  CHANGED" {
  exit 5 }
  "closed by remote host." {
  exit 6 }
  "Broken pipe" {
  exit 7 }
 }
expect {
"assword:" {
send "$password
" }
timeout {
exit 7 }
}
set timeout 3600
expect_before {
"assword:" {
exit 6 }
"Connection Refused" {
exit 1 }
"not found." {
exit 2 }
"Permission denied" {
exit 3 }
"Broken pipe" {
exit 4 }
closed by remote host." {
exit 5 }
}
expect {
"sftp>" { }
timeout { exit 7 }
}
send "ls -l /sample_directory/
"
expect "sftp>"
send "bye
"