SubContentID will only be set for subcontent in SCS and Summary if you edit the content type.
Therefore we must bump minor versions for SCS and Summary with accompanying UpgradeScripts that sets the UUID for old content.
All libraries that has dependencies to Summary or SCS must also be bumped.
A way to create UUID can be found at https://github.com/h5p/h5p-php-library/blob/master/js/h5p.js#L1737-L1742. Make sure that everything the upgradescript depends on lives within the script, it should not use any external functions.
Upgrade scripts for SCS and Summary