You need to do something like this to clear it:
while(openssl_error_string() !== false);
Some openssl functions will add errors to the list even if they succeed.
(PHP 4 >= 4.0.6, PHP 5, PHP 7)
openssl_error_string — Return openSSL error message
openssl_error_string() returns the last error from the openSSL library. Error messages are queued, so this function should be called multiple times to collect all of the information. The last error will be the most recent one.
Returns an error message string, or FALSE if there are no more error
messages to return.
Example #1 openssl_error_string() example
<?php
// lets assume you just called an openssl function that failed
while ($msg = openssl_error_string())
echo $msg . "<br />\n";
?>
You need to do something like this to clear it:
while(openssl_error_string() !== false);
Some openssl functions will add errors to the list even if they succeed.
Note that there may be two (or more) lines for one error.
Best to clear it out and read it for each openssl call.
PS
There are no "threads" and if the other library doesn't have enough sense to read (and therefore clear) the queue (errr, dequeue) of messages before and after their openssl calls...
A) That's their problem
B) Look for a new library, because NOT doing that means they aren't writing their code properly.