Why does substr give different results on different hostings?

Question

PHP

On one of the hostings, it is not clear how substr considers,

for example, there is

$c = base64_decode('Q1lv29m7u1cC7sojEM7iU9b0SibpRlrd/csYM2D5Z9BuWMY9EtDBJ8ynmPNmJVtvMRbtz5jCc17bZpqe/bEaiTdo1e9XviOJRMA4/8bFPV0=');
  $iv = substr($c, 0, 16);

string(23) "CYoٻW#SJ&FZ"
and on another hosting the result is
string(16) "CYoٻW#S"