If you go to the admin menu, it shows you which of the apps are not compatible with the new major version. Many apps are from volunteers and each of them needs to update, we try to anticipate and motivate people to help out and test:
What you can do:
if you have automatized your backups as well, you can perhaps revert to the previous version easily and check out the apps you are using first.
If not, you can try to disable these apps, and check if they are working on a version for NC28 and once they are released you can activate them again.