Failed Ajax request or invalid JSON returned - OJS 3.3.0.8

After updating my OJS to 3.3.0.8, when adding new avaliators to an article, i get multiple times the error “Failed Ajax request or invalid JSON returned”.

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The only solution i foung is to keep trying and sometimes it gets thru and shows the available avaliators.

Here is the php error log:

[07-Jul-2022 15:04:29 America/Sao_Paulo] PHP Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php:115
Stack trace:
#0 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php(115): PDOStatement->execute(NULL)
#1 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php(370): Doctrine\DBAL\Driver\PDOStatement->execute()
#2 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php(664): Illuminate\Database\Connection->Illuminate\Database{closure}(Object(Illuminate\Database\Query\Expression), Array)
#3 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php(745): Illuminate\Database\Connection->runQueryCallback(Object(Illuminate\Database\Query\Expression), Array, Object(Closure))
#4 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/fram in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php on line 671
[07-Jul-2022 15:05:29 America/Sao_Paulo] PHP Warning: PDOStatement::execute(): MySQL server has gone away in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php on line 115
[07-Jul-2022 15:05:29 America/Sao_Paulo] PHP Warning: PDOStatement::execute(): Error reading result set’s header in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php on line 115
[07-Jul-2022 15:06:14 America/Sao_Paulo] PHP Warning: PDOStatement::execute(): MySQL server has gone away in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php on line 115
[07-Jul-2022 15:06:14 America/Sao_Paulo] PHP Warning: PDOStatement::execute(): Error reading result set’s header in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php on line 115
[07-Jul-2022 15:06:14 America/Sao_Paulo] PHP Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php:115
Stack trace:
#0 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php(115): PDOStatement->execute(NULL)
#1 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php(370): Doctrine\DBAL\Driver\PDOStatement->execute()
#2 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php(664): Illuminate\Database\Connection->Illuminate\Database{closure}(Object(Illuminate\Database\Query\Expression), Array)
#3 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php(745): Illuminate\Database\Connection->runQueryCallback(Object(Illuminate\Database\Query\Expression), Array, Object(Closure))
#4 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/fram in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php on line 671
[07-Jul-2022 15:06:59 America/Sao_Paulo] PHP Warning: PDOStatement::execute(): MySQL server has gone away in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php on line 115
[07-Jul-2022 15:06:59 America/Sao_Paulo] PHP Warning: PDOStatement::execute(): Error reading result set’s header in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php on line 115
[07-Jul-2022 15:07:44 America/Sao_Paulo] PHP Warning: PDOStatement::execute(): MySQL server has gone away in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php on line 115
[07-Jul-2022 15:07:44 America/Sao_Paulo] PHP Warning: PDOStatement::execute(): Error reading result set’s header in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php on line 115
[07-Jul-2022 15:07:44 America/Sao_Paulo] PHP Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 2006 MySQL server has gone away in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php:115
Stack trace:
#0 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php(115): PDOStatement->execute(NULL)
#1 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php(370): Doctrine\DBAL\Driver\PDOStatement->execute()
#2 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php(664): Illuminate\Database\Connection->Illuminate\Database{closure}(Object(Illuminate\Database\Query\Expression), Array)
#3 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php(745): Illuminate\Database\Connection->runQueryCallback(Object(Illuminate\Database\Query\Expression), Array, Object(Closure))
#4 /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/fram in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php on line 671
[07-Jul-2022 15:08:44 America/Sao_Paulo] PHP Warning: PDOStatement::execute(): MySQL server has gone away in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php on line 115
[07-Jul-2022 15:08:44 America/Sao_Paulo] PHP Warning: PDOStatement::execute(): Error reading result set’s header in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php on line 115
[07-Jul-2022 15:10:14 America/Sao_Paulo] PHP Warning: PDOStatement::execute(): MySQL server has gone away in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php on line 115
[07-Jul-2022 15:10:14 America/Sao_Paulo] PHP Warning: PDOStatement::execute(): Error reading result set’s header in /home/dpgpsifp/psicodebate/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php on line 115

I found a similar topic, but with no answer: OJS 3.2 error: Failed Ajax request or invalid JSON returned

Hi @Hugo_Melo

Your error_log file shows that your DB is closing the connection to your application. The thread below shows some suggestions to fix it:

Best,
Israel

Well, for the record, I updated the version of php in the site, from 7.3 to 7.4 and the error frequency got lower, but persists.
I will try further versions of php…

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