While upgrading your Kayako Classic software, you may encounter an issue where the upgrade process gets stuck on the "App: tickets" step for several hours. You may also encounter this problem if the size of the database you are upgrading is in gigabytes.
The most common reason why this condition occurs is due to the server does not meet the required configuration specifically the PHP/MySQL Parameters.
To resolve this issue, make sure you follow the recommended PHP/MySQL Parameters configuration values from the Kayako Classic Server Configuration and System Requirements article. The values specified in the KB would allow the server to allocate a good amount of resources during the installation or upgrade which should prevent it from getting stuck on the "Apps: tickets" step.
The values that you should pay attention to are for the following parameters:
NOTE: The bottom line is that when installing or upgrading Kayako Classic, all specifications in the aforesaid article should be followed and met to avoid issues during the installation process.