phpBB fails after upgrade from MariaDB5 to MariaDB10 - Custom Synology package

My phpBB installation on Synology DSM 6.1 (latest version) fails after the upgrade from MariaDB5 to MariaDB10. I've already put a detailed failure description here: https://www.phpbb.com/community/viewtopic.php?f=556&t=2441286

I now tried to modify the official Synology package from https://archive.synology.com/download/Package/spk/phpBB/ according to the description on this site: https://amigotechnotes.wordpress.com/2014/05/17/how-to-create-a-spk-for-synology-dsm-to-distribute-your-lamp/

Actually, it didn't work...

I'm getting a "Package is invalid" or something like that in the Synology Package Station when installing from the generated SPK file.

Can anyone look at the repository https://github.com/SeppPenner/PhpBBFixMariaDB5Issue and check where the issue exactly is?

I finally found a solution: https://www.phpbb.com/community/viewtopic.php?f=556&t=2441286&p=14906311#p14906311

1. Install both database versions (MariaDB 5 and 10).
2. Import the whole mysql dump from before.
3. Add the same users (root) to both database versions.
4. Install phpBB on Synology package center with the passwords and a user for phpBB with some password.
5. I got an error: Database already exists" --> Dropped database for phpBB in MariaDB10.
6. Install was successful.
7. Uninstalled MariaDB5.
8. The board works again but posting is not possible. (There are some forum posts on this issue already and I will try to find a solution for this, too.)