Call Stored Procedure from PHP server scripts

Hello,
I have installed Dream Factory from github v 2.14.0, I use service with MariaDB service.

In php server script I call StoredProcedure with parameters. First call is ok, but second and others finish with error in DF log:
local.ERROR: Call to a member function prepare() on null {"exception":"[object] (Symfony\\Component\\Debug\\Exception\\FatalThrowableError(code: 0): Call to a member function prepare() on null at /opt/dreamfactory/dreamfactory_devel/vendor/dreamfactory/df-database/src/Components/Schema.php:1388)"}

As I looked in the code, it seems that $ this-> connection is NULL or $ this-> connection-> getPdo () is NULL. It looks like after the first call, the database connection is released.

After cleared cache, the call is working again for the first time, but next time it is with the same error again.

Do you have the similar problems?