this is my first question at this forum!
Circumstances are M2 2.2.7 on CentOS 7 with PHP 7.1 + all 3 types of caches managed by Redis 3.2.12 (on instance per type of cache). MySQL 5.latest and a couple of well-known 3rd party modules. Setup as per M2 DevDocs recommendations.
I am experiencing intermittent exceptions in vendor/magento/framework/session/SaveHandler.php; typically by the following signature:
"PHP Fatal error: Class Magento\Framework\Session\SaveHandler contains 2 abstract methods and must therefore be declared abstract or implement the remaining methods (SessionHandlerInterface::(...)".
The area failing seems to be random, it can be a 3rd party module, it can be M2 core modules (like magento-sales), the number of "abstract methods" can vary from 1 - 5.
Trying to refresh the page typically generates the following: "PHP Fatal error: Class Zend\Stdlib\Parameters contains 5 abstract methods and must therefore be declared abstract or implement the remaining methods (ArrayAccess::offsetExists, ArrayAccess::offsetSet, ArrayAccess::offsetUnset, ...) in [DocumentRoot]/vendor/zendframework/zend-stdlib/src/Parameters.php on line 14, (...)"
Contiuous refreshes can give: "PHP Fatal error: Class Zend\Stdlib\Parameters contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (Countable::count) in [DocumentRoot]/vendor/zendframework/zend-stdlib/src/Parameters.php on line 14"
When the system was transferred to the current server, these exceptions were very frequent. After about 5 minutes of operation, they started to appear.
After changing permissions to 777 on app/etc, generated, pub and var, they are much more rare and after setting the parameter "innodb_lock_wait_timeout" from default "50" to "7200", the exceptions now start to appear after about 2,5 - 4 hours.
A "systemctl restart httpd" seems to mitigate the situation.
I am in the dark here, starting to enter a state of apathy and considering switchin platform from M2 to something less complex.
I like Magento though so any suggestions on further mitigating activities or even the root cause would be highly appreciated.