You’re all good so far, your separate 8.17 branch is working fine. Now you can get your app’s main branch from 7.9 to 8.17 following these steps:
Hi Arne – first create another branch of the mainline and stet by step upgrade it to 8.17.
Merge this once tested into your mainline. And merge your modification branch line 8.17 into your mainline 8.17.
Regards, Boris