Intermittently empty primaryKey in Yii. What can be wrong?

Question

Yii

Hello. After updating the CentOS 7 server, and in particular PHP, MariaDB and others, I encountered anomalous behavior of the web application.
The bottom line is this:
on a page that works with one of the tables, I get the error

Invalid argument supplied for foreach() (/home/.yii-framework-1.1.16/db/ar/CActiveFinder.php:469)

This error occurs as a result of the table's primaryKey being empty:

if(is_string($this->_table->primaryKey))
      ...
    else
    {
      ...
      foreach($this->_table->primaryKey as $name)
      ...
    }

But, if I update any row of this table through the database manager, then in $this->_table->primaryKey we get the name of the column, as it should be. If I update the records again, the primaryKey is empty again! And so endlessly. update table - error - update table - works - update table - error - update table - works...
I just don't know where to dig. restart MariaDB also helps.
I can’t reload the database now, because this is prod. I'll try to raise a clone of the application on the same server.
What are your opinions?